Bone matrix compositions and methods

ABSTRACT

Osteoinductive compositions and implants having increased biological activities, and methods for their production, are provided. The biological activities that may be increased include, but are not limited to, bone forming; bone healing; osteoinductive activity, osteogenic activity, chondrogenic activity, wound healing activity, neurogenic activity, contraction-inducing activity, mitosisinducing activity, differentiation-inducing activity, chemotactic activity, angiogenic or vasculogenic activity, and exocytosis or endocytosis-inducing activity. In one embodiment, a method for producing an osteoinductive composition comprises providing partially demineralized bone, treating the partially demineralized bone to disrupt the collagen structure of the bone, and optionally providing a tissue-derived extract and adding the tissue-derived extract to the partially demineralized bone. In another embodiment, an implantable osteoinductive and osteoconductive composition comprises partially demineralized bone, wherein the collagen structure of the bone has been disrupted, and, optionally, a tissue-derived extract.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of U.S. Patent Application Ser. No.60/944,411 filed Jun. 15, 2007; U.S. Patent Application Ser. No.60/948,979 filed Jul. 10, 2007; and U.S. Patent Application Ser. No.60/957,614 filed Aug. 23, 2007, the contents of which are incorporatedin its entirety by reference herein.

BACKGROUND Introduction

Mammalian bone tissue is known to contain one or more proteinaceousmaterials, presumably active during growth and natural bone healing,that can induce a developmental cascade of cellular events resulting inendochondral bone formation. The active factors have variously beenreferred to in the literature as bone morphogenetic or morphogenicproteins (BMPs), bone inductive proteins, bone growth or growth factors,osteogenic proteins, or osteoinductive proteins. These active factorsare collectively referred to herein as osteoinductive factors.

It is well known that bone contains these osteoinductive factors. Theseosteoinductive factors are present within the compound structure ofcortical bone and are present at very low concentrations, e.g., 0.003%.Osteoinductive factors direct the differentiation of pluripotentialmesenchymal cells into osteoprogenitor cells that form osteoblasts.Based upon the work of Marshall Urist as shown in U.S. Pat. No.4,294,753, issued Oct. 13, 1981, proper demineralization of corticalbone exposes the osteoinductive factors, rendering it osteoinductive, asdiscussed more fully below.

Overview of Bone Grafts

The rapid and effective repair of bone defects caused by injury,disease, wounds, or surgery is a goal of orthopaedic surgery. Towardthis end, a number of compositions and materials have been used orproposed for use in the repair of bone defects. The biological,physical, and mechanical properties of the compositions and materialsare among the major factors influencing their suitability andperformance in various orthopaedic applications.

Autologous cancellous bone (“ACB”), also known as autograft orautogenous bone, long has been considered the gold standard for bonegrafts. ACB is osteoinductive and nonimmunogenic, and, by definition,has all of the appropriate structural and functional characteristicsappropriate for the particular recipient. Unfortunately, ACB is onlyavailable in a limited number of circumstances. Some individuals lackACB of appropriate dimensions and quality for transplantation, and donorsite pain and morbidity can pose serious problems for patients and theirphysicians.

Bone grafting applications are differentiated by the requirements of theskeletal site. Certain applications require a “structural graft” inwhich one role of the graft is to provide mechanical or structuralsupport to the site. Such grafts contain a substantial portion ofmineralized bone tissue to provide the strength needed for load-bearing.Examples of applications requiring a “structural graft” includeintercalary grafts, spinal fusion, joint plateaus, joint fusions, largebone reconstructions, etc. Other applications require an “osteogenicgraft” in which one role of the graft is to enhance or accelerate thegrowth of new bone tissue at the site. Such grafts contain a substantialportion of demineralized bone tissue to improve the osteoinductivityneeded for growth of new bone tissue. Examples of applications requiring“osteogenic graft” include deficit filling, spinal fusions, jointfusions, etc. Grafts may also have other beneficial biologicalproperties, such as, for example, serving as delivery vehicles forbioactive substances. Bioactive substances include physiologically orpharmacologically active substances that act locally or systemically inthe host.

When mineralized bone is used in osteoimplants, it is primarily becauseof its inherent strength, i.e., its load-bearing ability at therecipient site. The biomechanical properties of osteoimplants uponimplantation are determined by many factors, including the specific sitefrom which the bone used to make the osteoimplant is taken; variousphysical characteristics of the donor tissue; and the method chosen toprepare, preserve, and store the bone prior to implantation, as well asthe type of loading to which the graft is subjected.

Structural osteoimplants are conventionally made by processing, and thenmachining or otherwise shaping cortical bones collected for transplantpurposes. Osteoimplants may comprise monolithic bone of an aggregate ofparticles. Further, osteoimplants may be substantially solid, flowable,or moldable. Cortical bone can be configured into a wide variety ofconfigurations depending on the particular application for thestructural osteoimplant. Structural osteoimplants are often providedwith intricate geometries, e.g., series of steps; concave or convexsurfaces; tapered surfaces; flat surfaces; surfaces for engagingcorresponding surfaces of adjacent bone, tools, or implants, hex shapedrecesses, threaded holes; serrations, etc.

One problem associated with many monolithic structural osteoimplants,particularly those comprising cortical bone, is that they are neverfully incorporated by remodeling and replacement with host tissue. Sincerepair is a cellular-mediated process, dead (non-cellular, allograft orxenograft) bone is unable to repair itself. When the graft is penetratedby host cells and host tissue is formed, the graft is then capable ofrepair. It has been observed that fatigue damage is usually the resultof a buildup of unrepaired damage in the tissue. Therefore, to theextent that the implant is incorporated and replaced by living host bonetissue, the body can then recognize and repair damage, thus eliminatingfailure by fatigue. In applications where the mechanical load-bearingrequirements of the osteoimplant are challenging, e.g., intervertebralspinal implants for spinal fusion, lack of substantially completereplacement by host bone tissue may compromise the osteoimplant bysubjecting it to repeated loading and cumulative unrepaired damage inthe tissue (mechanical fatigue) within the implant material. Thus, it isdesirable that the osteoimplant has the capacity to support loadinitially and be capable of gradually transferring this load to the hostbone tissue as it remodels the implant.

Much effort has been invested in the identification and development ofalternative bone graft materials. Urist published seminal articles onthe theory of bone induction and a method for decalcifying bone, i.e.,making demineralized bone matrix (DBM). Urist M. R., Bone Formation byAutoinduction, Science 1965; 150(698):893-9; Urist M. R. et al., TheBone Induction Principle, Clin. Orthop. Rel. Res. 53:243-283, 1967. DBMis an osteoinductive material in that it induces bone growth whenimplanted in an ectopic site of a rodent, owing to the osteoinductivefactors contained within the DBM. It is now known that there arenumerous osteoinductive factors, e.g., BMP2, BMP4, BMP6, BMP7, which arepart of the transforming growth factor-beta (TGF-beta) superfamily.BMP-2 has become the most important and widely studied of the BMP familyof proteins. There are also other proteins present in DBM that are notosteoinductive alone but still contribute to bone growth, includingfibroblast growth factor-2 (FGF-2), insulin-like growth factor-I and -II(IGF-I and IGF-II), platelet derived growth factor (PDGF), andtransforming growth factor-beta 1 (TGF-beta.1).

Accordingly, a known technique for promoting the process ofincorporation of osteoimplants is demineralization of portions of, orthe entire volume of, the implant. The process of demineralizing bonegrafts is well known. In this regard see, Lewandrowski et al., J. BiomedMaterials Res, 31, pp. 365 372 (1996); Lewandrowski et al., CalcifiedTiss. Int., 61, pp. 294 297 (1997); Lewandrowski et al., J. Ortho. Res.,15, pp. 748 756 (1997), the contents of each of which is incorporatedherein by reference.

DBM implants have been reported to be particularly useful (see, forexample, U.S. Pat. Nos. 4,394,370, 4,440,750, 4,485,097, 4,678,470, and4,743,259; Mulliken et al., Calcif Tissue Int. 33:71, 1981; Neigel etal., Opthal. Plast. Reconstr. Surg. 12:108, 1996; Whiteman et al., J.Hand. Surg. 18B:487, 1993; Xiaobo et al., Clin. Orthop. 293:360, 1993,each of which is incorporated herein by reference). DBM typically isderived from cadavers. The bone is removed aseptically and treated tokill any infectious agents. The bone is particulated by milling orgrinding, and then the mineral component is extracted by variousmethods, such as by soaking the bone in an acidic solution. Theremaining matrix is malleable and can be further processed and/or formedand shaped for implantation into a particular site in the recipient. Thedemineralized bone particles or fibers can be formulated withbiocompatible excipients to enhance surgical handling properties andconformability to the defect or surgery site. Demineralized boneprepared in this manner contains a variety of components includingproteins, glycoproteins, growth factors, and proteoglycans. Followingimplantation, the presence of DBM induces cellular recruitment to thesite of injury. The recruited cells may eventually differentiate intobone forming cells. Such recruitment of cells leads to an increase inthe rate of wound healing and, therefore, to faster recovery for thepatient.

Demineralization provides the osteoimplant, whether monolithic,aggregate, flowable, or moldable, with a degree of flexibility. However,removal of the mineral components of bone significantly reducesmechanical strength of bone tissue. See, Lewandrowski et al., ClinicalOrtho. Rel. Res., 317, pp. 254 262 (1995). Thus, demineralizationsacrifices some of the load-bearing capacity of cortical bone and assuch may not be suitable for all osteoimplant designs.

While the collagen-based matrix of DBM is relatively stable, theosteoinductive factors within the DBM matrix are rapidly degraded. Theosteogenic activity of the DBM may be significantly degraded within 24hours after implantation, and in some instances the osteogenic activitymay be inactivated within 6 hours. Therefore, the osteoinductive factorsassociated with the DBM are only available to recruit cells to the siteof injury for a short time after transplantation. For much of thehealing process, which may take weeks to months, the implanted materialmay provide little or no assistance in recruiting cells. Further, mostDBM formulations are not load-bearing.

Extracting Proteins

The potential utility of osteoinductive factors has been recognizedwidely. It has been contemplated that the availability of osteoinductivefactors could revolutionize orthopedic medicine and certain types ofplastic surgery, dental, and various periodontal and craniofacialreconstructive procedures.

Urist's U.S. Pat. No. 4,294,753, herein incorporated by reference, wasthe first of many patents on a process for extracting BMP from DBM. Atthe time of the Urist '753 patent, BMP was referred to generally. It isnow known that there are multiple forms of BMP. The Urist process becamewidely adopted, and though different users may use different chemicalagents from those disclosed in the basic Urist process, the basic layoutof the steps of the process remains widely used today as one of the mainmethods of extracting BMP from DBM. See, e.g., U.S. Pub 2003/0065392(2003); U.S. Pub 2002/0197297 (2002). Urist reported that his basicprocess actually results in generally low yields of BMP per unit weightof DBM.

Implanting Extracted Proteins

Successful implantation of the osteoinductive factors for endochondralbone formation requires association of the proteins with a suitablecarrier material capable of maintaining the proteins at an in vivo siteof application. The carrier generally is biocompatible, in vivobiodegradable, and sufficiently porous to allow cell infiltration.Insoluble collagen particles that remain after guanidine extraction anddilapidation of pulverized bone generally have been found effective inallogenic implants in some species. However, studies have shown thatwhile osteoinductive proteins are useful cross species, the collagenousbone matrix generally used for inducing endochondral bone formation isspecies-specific. Sampath and Reddi, (1983) Proc. Nat. Acad. Sci. USA80: 6591-6594.

European Patent Application Serial No. 309,241, published Mar. 29, 1989,herein incorporated by reference, discloses a device for inducingendochondral bone formation comprising an osteogenic proteinpreparation, and a matrix carrier comprising 60-98% of either mineralcomponent or bone collagen powder and 2-40% atelopeptide hypoimmunogeniccollagen.

The use of pulverized exogenous bone growth material, e.g., derived fromdemineralized allogenic or xenogenic bone, in the surgical repair orreconstruction of defective or diseased bone in human or othermammalian/vertebrate species is known. See, in this regard, thedisclosures of U.S. Pat. Nos. 4,394,370, 4,440,750, 4,472,840,4,485,097, 4,678,470, 4,743,259, 5,284,655, 5,290,558; Bolander et al.,“The Use of Demineralized Bone Matrix in the Repair of SegmentalDefects,” The Journal of Bone and Joint Surgery, Vol. 68-A, No. 8, pp.1264-1273; Glowacki et al, “Demineralized Bone Implants,” Symposium onHorizons in Plastic Surgery, Vol. 12, No. 2; pp. 233-241 (1985);Gepstein et al., “Bridging Large Defects in Bone by Demineralized BoneMatrix in the Form of a Powder,” The Journal of Bone and Joint Surgery,Vol. 69-A, No. 7, pp. 984-991 (1987); Mellonig, “DecalcifiedFreeze-Dried Bone Allograft as an Implant Material In Human PeriodontalDefects,” The International Journal of Periodontics and RestorativeDentistry, pp. 41-45 (June 1984); Kaban et al., “Treatment of JawDefects with Demineralized Bone Implants,” Journal of Oral andMaxillofacial Surgery, pp. 623-626 (Jun. 6, 1989); and Todescan et al.,“A Small Animal Model for Investigating Endosseous Dental Implants:Effect of Graft Materials on Healing of Endosseous, Porous-SurfacedImplants Placed in a Fresh Extraction Socket,” The International Journalof Oral & Maxillofacial Implants Vol. 2, No. 4, pp. 217-223 (1987), allherein incorporated by reference.

A variety of approaches have been explored in an attempt to recruitprogenitor cells or chondrocytes into an osteochondral or chondraldefect. For example, penetration of subchondral bone has been performedin order to access mesenchymal stem cells (MSCs) in the bone marrow,which have the potential to differentiate into cartilage and bone.Steadman, et al., “Microfracture: Surgical Technique and Rehabilitationto Treat Chondral Defects,” Clin. Orthop., 391 S:362-369 (2001). Inaddition, some factors in the body are believed to aid in the repair ofcartilage. For example, transforming growth factors beta (TGF-β) havethe capacity to recruit progenitor cells into a chondral defect from thesynovium or elsewhere when loaded in the defect. Hunziker, et al.,“Repair of Partial Thickness Defects in Articular Cartilage: CellRecruitment From the Synovial Membrane,” J Bone Joint Surg.,78-A:721-733 (1996). However, the application of growth factors to boneand cartilage implants has not resulted in the expected increase inosteoinductive or chondrogenic activity.

U.S. Pat. No. 7,132,110, herein incorporated by reference, describes anosteogenic composition prepared by a process including the steps ofsubjecting demineralized bone to an extraction medium to produce aninsoluble extraction product and a soluble extraction product,separating the insoluble extraction product and the soluble extractionproduct, drying the soluble extraction product to remove all orsubstantially all of the moisture in the soluble extraction product, andcombining the dried soluble extraction product with demineralized boneparticles. Studies using the process have shown that the formedosteogenic composition does not have appreciably increasedosteoinductive properties when compared to the demineralized boneparticles to which the dried soluble extraction product is added. It wasfurther determined that the demineralized bone from which the extractionproducts are extracted does not exhibit appreciably decreasedosteoinductive properties when compared with its properties prior toextraction. It is thus theorized that the extraction process withdrawsonly a small fraction of available tissue repair factors.

Overall, current bone and cartilage graft formulations have variousdrawbacks. The osteoinductive factors within the matrices can be rapidlydegraded and, thus, factors associated with the matrix are onlyavailable to recruit cells to the site of injury for a short time afterimplantation. Further, in certain instances the current graftformulations exhibit limited capacity to stimulate tissue formation.

BRIEF SUMMARY

Osteoinductive compositions and implants having increased biologicalactivities, and methods for their production, are provided. Thebiological activities that may be increased include, but are not limitedto, bone forming, bone healing, osteoinductive activity, osteogenicactivity, chondrogenic activity, wound healing activity, neurogenicactivity, contraction-inducing activity, mitosisinducing activity,differentiation-inducing activity, chemotactic activity, angiogenic orvasculogenic activity, and exocytosis or endocytosis-inducing activity.

In one embodiment, a method for producing an osteoinductive compositionis provided. The method comprises providing partially demineralizedbone, treating the partially demineralized bone to disrupt the collagenstructure of the bone, providing a tissue-derived extract, and addingthe tissue-derived extract to the partially demineralized bone.

In another embodiment, an implantable osteoinductive and osteoconductivecomposition is provided. The composition comprises partiallydemineralized bone, wherein the collagen structure of the bone has beendisrupted, and a tissue-derived extract.

In yet another embodiment, a method for producing an osteoinductivecomposition is provided. The method comprises providing surfacedemineralized bone and treating the surface demineralized bone todisrupt the collagen structure of the bone.

In a further embodiment, an implantable osteoinductive andosteoconductive composition is provided. The composition comprisessurface demineralized bone or substantially fully demineralized, whereinthe collagen structure of the bone has been disrupted.

In yet a further embodiment, a method for treating a bone condition isprovided. The method comprises providing partially demineralized bone,treating the partially demineralized bone to disrupt the collagenstructure of the bone, providing a tissue-derived extract, adding thetissue-derived extract to the partially demineralized bone, andimplanting the tissue-derived extract and partially demineralized bone.

In another embodiment, an osteoinductive composition is providedcomprising surface demineralized bone particles, the bone particlesranging from approximately 1 mm to approximately 4 mm in length, whereinthe collagen structure of the bone has been disrupted. Theosteoinductive composition further comprises demineralized bone matrixand tissue derived extract.

This application refers to various patents, patent applications, journalarticles, and other publications, all of which are incorporated hereinby reference. The following documents are incorporated herein byreference: PCT/US04/43999; PCT/US05/003092; US 2003/0143258 A1;PCT/US02/32941; Current Protocols in Molecular Biology, CurrentProtocols in Immunology, Current Protocols in Protein Science, andCurrent Protocols in Cell Biology, John Wiley & Sons, N.Y., edition asof July 2002; Sambrook, Russell, and Sambrook, Molecular Cloning: ALaboratory Manual, 3rd ed., Cold Spring Harbor Laboratory Press, ColdSpring Harbor, 2001; Rodd 1989 “Chemistry of Carbon Compounds,” vols.1-5 and supps, Elsevier Science Publishers, 1989; “Organic Reactions,”vols 1-40, John Wiley and Sons, New York, N.Y., 1991; March 2001,“Advanced Organic Chemistry,” 5th ed. John Wiley and Sons, New York,N.Y. In the event of a conflict between the specification and any of theincorporated references, the specification shall control. Wherenumerical values herein are expressed as a range, endpoints areincluded.

While multiple embodiments are disclosed, still other embodiments of thepresent invention will become apparent to those skilled in the art fromthe following detailed description. As will be apparent, the inventionis capable of modifications in various obvious aspects, all withoutdeparting from the spirit and scope of the present invention.Accordingly, the detailed description is to be regarded as illustrativein nature and not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a flowchart of a method for producing anosteoinductive composition in accordance with one embodiment.

FIG. 2 illustrates a flowchart of a method for producing osteoinductivebone in the absence of protease inhibitors in accordance with oneembodiment.

FIG. 3 illustrates a graph of neutral protease activity of mineralizedand demineralized bone.

FIG. 4 a illustrates a generally round bone particle wherein the boneparticle has been surface demineralized in accordance with oneembodiment.

FIG. 4 b illustrates an elongate bone particle wherein the bone particlehas been surface demineralized in accordance with one embodiment.

FIG. 5 comparatively illustrates site response of autograft implantsversus site response of surface demineralized heat treated particleimplants.

DEFINITIONS

Bioactive Agent or Bioactive Compound, as used herein, to refers to acompound or entity that alters, inhibits, activates, or otherwiseaffects biological or chemical events. For example, bioactive agents mayinclude, but are not limited to, osteogenic or chondrogenic proteins orpeptides, anti-AIDS substances, anti-cancer substances, antibiotics,immunosuppressants, anti-viral substances, enzyme inhibitors, hormones,neurotoxins, opioids, hypnotics, anti-histamines, lubricants,tranquilizers, anti-convulsants, muscle relaxants and anti-Parkinsonsubstances, anti-spasmodics and muscle contractants including channelblockers, miotics and anti-cholinergics, anti-glaucoma compounds,anti-parasite and/or anti-protozoal compounds, modulators ofcell-extracellular matrix interactions including cell growth inhibitorsand antiadhesion molecules, vasodilating agents, inhibitors of DNA, RNAor protein synthesis, anti-hypertensives, analgesics, anti-pyretics,steroidal and non-steroidal anti-inflammatory agents, anti-angiogenicfactors, angiogenic factors, anti-secretory factors, anticoagulantsand/or antithrombotic agents, local anesthetics, ophthalmics,prostaglandins, anti-depressants, anti-psychotic substances,anti-emetics, and imaging agents. In certain embodiments, the bioactiveagent is a drug. In some embodiments, the bioactive agent is a growthfactor, cytokine, extracellular matrix molecule or a fragment orderivative thereof, for example, a cell attachment sequence such as RGD.A more complete listing of bioactive agents and specific drugs suitablefor use in the present invention may be found in “PharmaceuticalSubstances: Syntheses, Patents, Applications” by Axel Kleemann andJurgen Engel, Thieme Medical Publishing, 1999; the “Merck Index: AnEncyclopedia of Chemicals, Drugs, and Biologicals”, Edited by SusanBudavari et al., CRC Press, 1996; and the United StatesPharmacopeia-25/National Formulary-20, published by the United StatesPharmacopeial Convention, Inc., Rockville Md., 2001, each of which isincorporated herein by reference.

Biocompatible, as used herein, refers to materials that, uponadministration in vivo, do not induce undesirable long-term effects.

Bone, as used herein, refers to bone that is cortical, cancellous orcortico-cancellous of autogenous, allogenic, xenogenic, or transgenicorigin.

Bone Fibers, as used herein, refer to elongate bone particles comprisingthreads or filaments having a median length to median thickness ratio ofat least about 10:1 and up to about 500:1, a median length of from about2 mm to about 400 mm, a medium width of about 2 mm to about 5 mm, and amedian thickness of from about 0.02 mm to about 2 mm.

Bone Particle, as used herein, refers to a piece of particulated bonewith wide range of average particle size ranging from relatively finepowders to coarse grains and even larger chips. For example, the boneparticles may range in average particle size from about 0.1 mm to about15 mm in its largest dimension, or from about 0.5 to about 1.0 mm. Thebone particles may be generally round and have a radius, may beelongated, may be irregular, or may be in any other suitableconfiguration. The bone particles can be obtained from about cortical,cancellous and/or corticocancellous autogenous, allogenic, xenogenic, ortransgenic bone tissue.

Demineralized, as used herein, refers to any material generated byremoving mineral material from tissue, e.g., bone tissue. In certainembodiments, the demineralized compositions described herein includepreparations containing less than 5% calcium. In some embodiments, thedemineralized compositions may comprise less than 1% calcium by weight.Partially demineralized bone is intended to refer to preparations withgreater than 5% calcium by weight but containing less than 100% of theoriginal starting amount of calcium. In some embodiments, demineralizedbone has less than 95% of its original mineral content. Percentage ofdemineralization may refer to percentage demineralized by weight, or topercentage demineralized by depth, as described with reference to FIGS.4 a and 4 b. “Demineralized” is intended to encompass such expressionsas “substantially demineralized,” “partially demineralized,” “surfacedemineralized,” and “fully demineralized.” “Partially demineralized” isintended to encompass “surface demineralized.”

Demineralized bone matrix (DBM), as used herein, refers to any materialgenerated by removing mineral material from bone tissue. In someembodiments, the DBM compositions as used herein include preparationscontaining less than 5% calcium and preferably less than 1% calcium byweight. In other embodiments, the DBM compositions comprise partiallydemineralized bone (e.g., preparations with greater than 5% calcium byweight but containing less than 100% of the original starting amount ofcalcium).

Osteoconductive, as used herein, refers to the ability of anon-osteoinductive substance to serve as a suitable template orsubstance along which bone may grow.

Osteogenic, as used herein, refers to materials containing living cellscapable of differentiation into bone tissue.

Osteoimplant as used herein refers to any bone-derived implant preparedin accordance with the embodiments of this invention and therefore isintended to include expressions such as bone membrane, bone graft, etc.

Osteoinductive, as used herein, refers to the quality of being able torecruit cells from the host that have the potential to stimulate newbone formation. Any material that can induce the formation of ectopicbone in the soft tissue of an animal is considered osteoinductive. Forexample, most osteoinductive materials induce bone formation in athymicrats when assayed according to the method of Edwards et al.,“Osteoinduction of Human Demineralized Bone: Characterization in a RatModel,” Clinical Orthopaedics & Rel. Res., 357:219-228, December 1998,incorporated herein by reference. In other instances, osteoinduction isconsidered to occur through cellular recruitment and induction of therecruited cells to an osteogenic phenotype. Osteoinductivity scorerefers to a score ranging from 0 to 4 as determined according to themethod of Edwards et al. (1998) or an equivalent calibrated test. In themethod of Edwards et al., a score of “0” represents no new boneformation; “1” represents 1%-25% of implant involved in new boneformation; “2” represents 26-50% of implant involved in new boneformation; “3” represents 51%-75% of implant involved in new boneformation; and “4” represents >75% of implant involved in new boneformation. In most instances, the score is assessed 28 days afterimplantation. However, the osteoinductivity score may be obtained atearlier time points such as 7, 14, or 21 days following implantation. Inthese instances it may be desirable to include a normal DBM control suchas DBM powder without a carrier, and if possible, a positive controlsuch as BMP. Occasionally osteoinductivity may also be scored at latertimepoints such as 40, 60, or even 100 days following implantation.Percentage of osteoinductivity refers to an osteoinductivity score at agiven time point expressed as a percentage of activity, of a specifiedreference score. Osteoinductivity may be assessed in an athymic rat orin a human. Generally, as discussed herein, an osteoinductive score isassessed based on osteoinductivity in an athymic rat.

Pressed bone fibers, as used herein, refer to bone fibers formed byapplying pressure to bone stock. The bone utilized as the starting, orstock, material may range in size from relatively small pieces of boneto bone of such dimensions as to be recognizable as to its anatomicalorigin. The bone may be substantially fully demineralized, surfacedemineralized, partially demineralized, or nondemineralized. In general,the pieces or sections of whole bone stock can range from about 1 toabout 400 mm, from about 5 to about 100 mm, in median length, from about0.5 to about 20 mm, or from about 2 to about 10 mm, in median thicknessand from about 1 to about 20 mm, or from about 2 to about 10 mm, inmedian width. Forming bone fibers by pressing results in intact bonefibers of longer length than other methods of producing elongate bonefibers, with the bone fibers retaining more of the native collagenstructure. The bone may be particulated via pressure applied to thebone, as discussed in U.S. Pat. No. 7,323,193, herein incorporated byreference.

Proteases, as used herein, refers to protein-cleaving enzymes thatcleave peptide bonds that link amino acids in protein molecules togenerate peptides and protein fragments. A large collection of proteasesand protease families has been identified. Some exemplary proteasesinclude serine proteases, aspartyl proteases, acid proteases, alkalineproteases, metalloproteases, carboxypeptidase, aminopeptidase, cysteineprotease, collagenase, etc. An exemplary family of proteases is theproprotein convertase family, which includes furin. Dubois et al.,American Journal of Pathology (2001) 158(1):305-316. Members of theproprotein convertase family of proteases are known to proteolyticallyprocess proTGFs and proBMPs to their active mature forms. Dubois et al.,American Journal of Pathology (2001) 158(1):305-316; Cui et al., TheEmbo Journal (1998) 17(16):4735-4743; Cui et al., Genes & Development(2001) 15:2797-2802, each incorporated by reference herein.

Protease inhibitors, as used herein, refers to chemical compoundscapable of inhibiting the enzymatic activity of protein cleaving enzymes(i.e., proteases). The proteases inhibited by these compounds includeserine proteases, acid proteases, metalloproteases, carboxypeptidase,aminopeptidase, cysteine protease, etc. The protease inhibitor may actspecifically to inhibit only a specific protease or class of proteases,or it may act more generally by inhibiting most if not all proteases.Preferred protease inhibitors are protein or peptide based and arecommercially available from chemical companies such as Aldrich-Sigma.Protein or peptide-based inhibitors which adhere to the DBM (or calciumphosphate or ceramic carrier) may be preferred because they remainassociated with the matrix providing a stabilizing effect for a longerperiod of time than freely diffusible inhibitors. Examples of proteaseinhibitors include aprotinin, 4-(2-aminoethyl) benzenesulfonyl fluoride(AEBSF), amastatin-HC1, alpha1-antichymotrypsin, antithrombin III,alpha1-antitrypsin, 4-aminophenylmethane sulfonyl-fluoride (APMSF),arphamenine A, arphamenine B, E-64, bestatin, CA-074, CA-074-Me, calpaininhibitor I, calpain inhibitor II, cathepsin inhibitor, chymostatin,diisopropylfluorophosphate (DFP), dipeptidylpeptidase IV inhibitor,diprotin A, E-64c, E-64d, E-64, ebelactone A, ebelactone B, EGTA,elastatinal, foroxymithine, hirudin, leuhistin, leupeptin,alpha2macroglobulin, phenylmethylsulfonyl fluo4de (PMSF), pepstatin A,phebestin, 1,10phenanthroline, phosphoramidon, chymostatin, benzamidineHCl, antipain, epsilon aminocaproic acid, N-ethylmaleimide, trypsininhibitor, 1-chloro-3-tosylamido-7-amino-2-heptanone (TLCK),1-chloro-3-tosylamido-4-phenyl-2-butanone (TPCK), trypsin inhibitor, andsodium EDTA.

Stabilizing agent, as used herein, refers to any chemical entity that,when included in a composition comprising bone matrix and/or a growthfactor, enhances the osteoinductivity of the composition as measuredagainst a specified reference sample. In most cases, the referencesample will not contain the stabilizing agent, but in all other respectswill be the same as the composition with stabilizing agent. Thestabilizing agent also generally has little or no osteoinductivity ofits own and works either by increasing the half-life of one or more ofthe active entities within the composition as compared with an otherwiseidentical composition lacking the stabilizing agent, or by prolonging ordelaying the release of an active factor. In certain embodiments, thestabilizing agent may act by providing a barrier between proteases andsugar-degrading enzymes thereby protecting the osteoinductive factorsfound in or on the matrix from degradation and/or release. In otherembodiments, the stabilizing agent may be a chemical compound thatinhibits the activity of proteases or sugar-degrading enzymes. In someembodiments, the stabilizing agent retards the access of enzymes knownto release and solubilize the active factors. Half-life may bedetermined by immunological or enzymatic assay of a specific factor,either as attached to the matrix or extracted there from. Alternatively,measurement of an increase in osteoinductivity half-life, or measurementof the enhanced appearance of products of the osteoinductive process(e.g., bone, cartilage or osteogenic cells, products or indicatorsthereof) is a useful indicator of stabilizing effects for an enhancedosteoinductive matrix composition. The measurement of prolonged ordelayed appearance of a strong osteoinductive response will generally beindicative of an increase in stability of a factor coupled with adelayed unmasking of the factor activity.

Superficially demineralized, as used herein, refers to bone-derivedelements possessing at least about 90 weight percent of their originalinorganic mineral content, the expression “partially demineralized” asused herein refers to bone-derived elements possessing from about 8 toabout 90 weight percent of their original inorganic mineral content andthe expression “fully demineralized” as used herein refers to bonecontaining less than 8% of its original mineral context.

DETAILED DESCRIPTION I. Introduction

Osteoinductive compositions and implants and methods for theirproduction are provided. In various embodiments, the osteoinductivecompositions may comprise one or more of partially demineralized(including surface demineralized) bone particles treated to disrupt thecollagen structure, a tissue-derived material or extract, and a carrier.In some embodiments, the partially demineralized bone particles may notbe treated to disrupt the collagen structure. In some embodiments,demineralized bone matrix, such as demineralized bone fibers, may beadded to the treated partially demineralized bone particles. Thecombination of DBM and partially demineralized bone particles may thenfurther include a tissue-derived extract and/or a carrier. Those ofordinary skill will appreciate that a variety of embodiments or versionsof the invention are not specifically discussed below but arenonetheless within the scope of the present invention, as defined by theappended claims.

According to certain embodiments, partially demineralized bone particlesare exposed to a treatment or condition that increases at least onebiological activity of the partially demineralized bone particles. Atissue-derived extract may be added to the partially demineralized boneparticles. Alternatively, or additionally, the partially demineralizedbone particles may be added to a carrier. In some embodiments, thepartially demineralized bone particles may function as a carrier for thetissue-derived extract. In some embodiments, the partially demineralizedtreated particles may be used without addition of an extract or acarrier. In some embodiments, the partially demineralized particles maynot be treated.

In some embodiments, a method of producing autolyzed, antigen-extracted,allogenic bone in the absence of protease inhibitors is provided.

FIG. 1 illustrates a method 10 for producing an osteoinductivecomposition in accordance with a first embodiment. As shown, the methodcomprises particulating bone [block 12] and surface-demineralizing thebone particles [block 14]. The surface demineralized bone particles maybe treated to disrupt collagen structure of the bone [block 16]. Thetreatment may be done in any suitable manner and is discussed more fullybelow. In some embodiments, treatment of the surface demineralized boneparticles [block 16] is not done. A tissue-derived extract may added tothe surface-demineralized bone particles [block 18]. In someembodiments, the surface-demineralized bone particles may be combinedwith demineralized bone matrix, such as pressed demineralized bonefibers [block 17]. The surface-demineralized bone particles, with orwithout demineralized bone matrix or tissue derived extract, may be usedwith a delivery vehicle [block 19]. In one embodiment, the deliveryvehicle may be a carrier and the composition may be added to a carrier[block 20]. In another embodiment the delivery vehicle may be a coveringand the composition, including the surface-demineralized bone particles,pressed demineralized bone fibers, tissue derived extract, and/orcarrier, may be provided in a covering [block 22]. The composition,including delivery vehicle in some embodiments, may be used to treat abone defect [block 24].

In some embodiments, treatment of the surface of demineralized boneparticles [block 16] may disrupt collagen and growth factors of both theexterior and the interior of the bone particles. In other embodiments,collagen and growth factors of the exterior of the bone may be leftsubstantially intact while collagen and growth factors of the interiorof the bone are disrupted.

Surface demineralization of the bone substantially removes mineral andproteases from the surface of the bone. FIG. 3 is a graph showingneutral protease activity of mineralized and demineralized bone. Asshown, demineralized bone has significantly lower neutral proteaseactivity than mineralized bone. Demineralization prior to autolysis ortreatment of the bone reduces protease activity on the surfaces of theparticle. Accordingly, using treatment techniques that disrupt collagenand growth factors in the presence of proteases, for example, autolysis,surface collagen and growth factors are not disrupted ifdemineralization proceeds such treatment. In contrast, the growthfactors in the mineralized portion of the bone are disrupted during suchtreatment. The lower protease activity of the particle surfacesmaintains osteoinductive activity. Autolysis of the osteoconductivemineralized core of the particles causes the particles to exhibitreduced delayed hypersensitivity reaction. Thus, in accordance with someembodiments, a method of autolysis of bone and maintenance ofosteoinductive activity in the bone without requiring use of proteaseinhibitors.

FIG. 2 illustrates a method 30 of producing osteoinductive bone in theabsence of protease inhibitors. As shown in FIG. 2, bone particles areparticulated [block 32]. The bone particles may be particulated to anysuitable size ranging from microns to millimeters. In some embodiments,the particles are particulated to a size ranging from approximately 500microns to approximately 10 mm, from approximately 500 microns toapproximately 4 mm, or other size. In one embodiment, the bone particlesrange from between about 0.5 mm to about 15 mm in their longestdimension. The bone particles are delipidized [block 34]. Delipidizingthe bones may comprise delipidizing the bone in 70% to 100% ethanol formore than about 1 hour. Delipidizing the bones may also comprisedelipidizing bone in a critical or supercritical fluid such as carbondioxide. The delipidized bone particles are surface demineralized [block36], as described more fully below. The surface demineralizeddelipidized bone particles may optionally be treated to disrupt collagenby, for example, incubating in a phosphate buffer [block 38]. Theincubation may be done in any suitable manner, including, for example,at a pH of approximately 7.4, at approximately 37° C. for several hours(for example, ranging from approximately 2 hours to approximately 96hours). The particles may be treated to remove water, for example vialyophilization or critical point drying [block 37], and sterilized[block 39]. In some embodiments, removing water the particles may bedone prior to treating the surface demineralized bone particles todisrupt the collagen structure. Removing water from the particles may bereferred to as drying the particles or dehydrating the particles and maybe done to any suitable level. Sterilization may comprise, for example,treatment with supercritical carbon dioxide. The bone particles may beused with a delivery vehicle [block 40], such as by adding to a carrier[block 41] and/or placement in a covering [block 42].

In some embodiments, demineralized bone fibers may be combined with thebone particles in a delivery vehicle [block 43]. In some embodiments,the bone fibers are formed by pressing, described below. Prior tocombination with the particles, water may be removed from the bonefibers [block 45]. Drying of the pressed fibers may comprise, forexample, critical point drying. U.S. Pat. No. 7,323,193 for a Method ofMaking Demineralized Bone Particles, herein incorporated by reference,describes suitable methods for making pressed demineralized bone fibersthat may be used with the present invention.

The bone particles provided by the methods of FIG. 1 or 2 may becombined with tissue-derived extracts and/or carriers. In certainembodiments, the tissue-derived extract includes collagen type-I orcollagen type-I residues. Thus, the extract may contain peptides orprotein fragments that increase the osteoinductive or chondrogenicproperties of the partially demineralized bone particles. Bone is madeup principally of cells, and also of collagen, minerals, and othernoncollagenous proteins. Bone matrices can be nondemineralized,partially demineralized, demineralized, deorganified, anorganic, ormixtures of these. DBM is comprised principally of proteins andglycoproteins, collagen being the primary protein component of DBM.While collagen is relatively stable, normally being degraded only by therelatively rare collagenase enzymes, various other proteins and activefactors present in DBM are quickly degraded by enzymes present in thehost. These host-derived enzymes include proteases and sugar-degradingenzymes (e.g., endo- and exoglycosidases, glycanases, glycolases,amylase, pectinases, galacatosidases, etc.). Many of the active growthfactors responsible for the osteoinductive activity of DBM exist incryptic form, in the matrix until activated. Activation can involve thechange of a pre or pro function of the factor, release of the functionfrom a second factor or entity that binds to the first growth factor, orexposing the BMPs to make them available at the outer surface of theDBM. Thus, growth factor proteins in a DBM or added to a DBM may have alimited osteoinductive effect because they are rapidly inactivated bythe proteolytic environment of the implant site, or even within the DBMitself.

A number of endogenous factors that play important roles in thedevelopment and/or repair of bone and/or cartilage have been identified.BMPs such as BMP-2 and BMP-4 induce differentiation of mesenchymal cellstowards cells of the osteoblastic lineage, thereby increasing the poolof mature cells, and also enhance the functions characteristic ofdifferentiated osteoblasts. Canalis et al., Endocrine Rev.24(2):218-235, 2003, herein incorporated by reference. In addition, BMPsinduce endochondral ossification and chondrogenesis. BMPs act by bindingto specific receptors, which results in phosphorylation of a class ofproteins referred to as SMADs. Activated SMADs enter the nucleus, wherethey regulate transcription of particular target genes. BMPs alsoactivate SMAD-independent pathways such as those involving Ras/MAPKsignaling. Unlike most BMPs such as BMP-2 and BMP-4, certain BMPs (e.g.,BMP-3) act as negative regulators (inhibitors) of osteogenesis. Inaddition, BMP-1 is distinct both structurally and in terms of itsmechanism of action from other BMPs, which are members of the TGF-βsuperfamily. Unlike certain other BMPs (e.g., BMP-2, BMP-4), BMP-1 isnot osteoinductive. Instead, BMP-1 is a collagenolytic protein that hasalso been shown to cleave chordin (an endogenous inhibitor of BMP-2 andBMP-4). Tolloid is a metalloprotease that is structurally related toBMP-1 and has proteolytic activity towards chordin. See Canalis, supra,for further details regarding the activities of BMPs and their roles inosteogenesis and chondrogenesis.

A variety of endogenous inhibitors of BMPs have been discovered inaddition to chordin. These proteins act as BMP antagonists and includepseudoreceptors (e.g., Bambi) that compete with signaling receptors,inhibitory SMADs that block signaling, intracellular binding proteinsthat bind to activating SMADs, factors that induce ubiquitination andproteolysis of activating SMADs, and extracellular proteins that bindBMPs and prevent their binding to signaling receptors. Among theextracellular proteins are noggin, chordin, follistatin, members of theDan/Cerberus family, and twisted gastrulation.

II. Implantable Osteoinductive/Osteoconductive Composition

An implantable osteoinductive composition and methods for preparing suchcomposition are provided. The osteoinductive composition has anincreased biological activity compared to other demineralized bone. Forexample, the composition may have inductivity exceeding that of fromgreater than one to about two to about five equivalent volumes ofdemineralized bone prepared by traditional, prior art methods. Theosteoinductive composition may be formed into an implant and/or may beprovided in a delivery vehicle.

The biological activities of the composition that may be increasedinclude but are not limited to osteoinductive activity, osteogenicactivity, chondrogenic activity, wound healing activity, neurogenicactivity, contraction-inducing activity, mitosis-inducing activity,differentiation-inducing activity, chemotactic activity, angiogenic orvasculogenic activity, and exocytosis or endocytosis-inducing activity.It will be appreciated that bone formation processes frequently includea first stage of cartilage formation that creates the basic shape of thebone, which then becomes mineralized (endochondral bone formation).Thus, in many instances, chondrogenesis may be considered an early stageof osteogenesis, though of course it may also occur in other contexts.

The osteoinductive composition may comprise all or some of partiallydemineralized bone particles, demineralized bone fibers, atissue-derived extract, and a delivery vehicle. The osteoinductivecomposition provides concentrated or enhanced osteoinductive activity.In some embodiments, the osteoinductive composition is prepared byproviding partially demineralized bone, optionally treating thepartially demineralized bone, extracting osteoinductive factors fromtissue, and adding the extracted osteoinductive factors to the partiallydemineralized bone. The partially demineralized bone and extract may beadded to a delivery vehicle such as a carrier or a covering. In otherembodiments, the osteoinductive composition is prepared by providedpartially demineralized bone particles (which may be in the form ofchips), providing pressed demineralized bone fibers, and combining thepartially demineralized bone particles and pressed demineralized bonefibers, for example in a delivery vehicle. The partially demineralizedbone, pressed demineralized bone fibers, extract, and delivery vehiclemay form an osteoimplant. The osteoimplant, when implanted in amammalian body, can induce at the locus of the implant the fulldevelopmental cascade of endochondral bone formation includingvascularization, mineralization, and bone marrow differentiation. Also,in some embodiments, the osteoinductive composition can be used as adelivery device to administer bioactive agents.

In some embodiments, the partially demineralized bone may comprise thedelivery vehicle by forming a carrier. In certain embodiments, thecarrier contains peptides or protein fragments that increase itsosteoinductive or chondrogenic properties. In some embodiments, thecarrier comprises the remaining matrix after extraction. Thetissue-derived extract, for example, peptides or protein fragments, maybe exogenously added to the carrier. Further, other agents may be addedto the carrier and/or to the partially demineralized bone, e.g., agentsthat improve the osteogenic and/or chondrogenic activity of thepartially demineralized bone by either transcriptional orpost-transcriptional regulation of the synthesis of bone or cartilageenhancing or inhibiting factors by cells within the carrier.

III. Provide Partially Demineralized Bone

In some embodiments, demineralized bone that is substantially fullydemineralized is used. In other embodiments, partially demineralizedbone is used. In other embodiments, the surface demineralized bone isused. In other embodiments, nondemineralized bone may be used. In otherembodiments, combinations of some of all of the above may be used. Whilemany of the examples in this section refer to partially or surfacedemineralized bone, this is for illustrative purposes.

In one embodiment, the bone is partially demineralized. Referring toFIG. 1, the bone may be surface demineralized [block 14]. The partiallydemineralized bone may be provided in any suitable manner. Generally,the bone may be obtained utilizing methods well known in the art, e.g.,allogenic donor bone. The partially demineralized bone may comprisemonolithic bone, bone particles, or other bone-derived elements. In someembodiments, the partially demineralized bone comprises partiallydemineralized bone particles. The particles may range in size from about0.5 mm to about 15 mm, from about 1 mm to about 10 mm, from about 1 mmto about 8 mm, from about 1 mm to about 4 mm, from about 0.5 mm to about4 mm, or other range, in their longest dimension. Bone-derived elementscan be readily obtained from donor bone by various suitable methods,e.g., as described in U.S. Pat. No. 6,616,698, incorporated herein byreference. The bone may be cortical, cancellous, or cortico-cancellousof autogenous, allogenic, xenogenic, or transgenic origin. Thedemineralized bone is referred to as partially demineralized for thepurposes of illustration. Partially demineralized bone as used hereinincludes surface demineralized bone.

As will be described, the bone may be particulated, demineralized, andtreated.

Demineralized bone matrix (DBM) preparations have been used for manyyears in orthopedic medicine to promote the formation of bone. Forexample, DBM has found use in the repair of fractures, in the fusion ofvertebrae, in joint replacement surgery, and in treating bonedestruction due to underlying disease such as rheumatoid arthritis. DBMis thought to promote bone formation in vivo by osteoconductive andosteoinductive processes. The osteoinductive effect of implanted DBMcompositions is thought to result from the presence of active growthfactors present on the isolated collagen-based matrix.

To provide the osteoinductive composition described herein, the bone istreated to remove mineral from the bone. Generally, the bone ispartially or surface demineralized. While hydrochloric acid is theindustry-recognized demineralization agent of choice, the literaturecontains numerous reports of methods for preparing DBM (see, forexample, Russell et al., Orthopaedics 22(5):524-531, May 1999;incorporated herein by reference). The partially demineralized bone maybe prepared by methods known in the art or by other methods that can bedeveloped by those of ordinary skill in the art without undueexperimentation. In some instances, large fragments or even whole ormonolithic bone may be demineralized. The whole or monolithic bone maybe used intact or may be particulated following demineralization. Inother embodiments, the bone may be particulated and then demineralized,as shown in FIG. 1.

Any suitable demineralization procedure may be used. In onedemineralization procedure, the bone is subjected to an aciddemineralization step followed by a defatting/disinfecting step. Thebone is immersed in acid over time to effect demineralization. Acidsthat can be employed in this step include inorganic acids such ashydrochloric acid and as well as organic acids such as formic acid,acetic acid, peracetic acid, citric acid, propionic acid, etc. The depthof demineralization into the bone surface can be controlled by adjustingthe treatment time, temperature of the demineralizing solution,concentration of the demineralizing solution, nature of thedemineralizing agent, agitation intensity during treatment, pressure ofthe demineralizing environment, and other forces applied to thedemineralizing solution or bone. The extent of demineralization may bealtered or controlled by varying size of the bone or bone particlesbeing demineralized, by varying concentration of the demineralizationacid, by varying temperature, by sonicating or applying vacuum duringdemineralization, or other.

The demineralized bone is rinsed with sterile water and/or bufferedsolution(s) to remove residual amounts of acid and thereby raise the pH.A suitable defatting/disinfectant solution is an aqueous solution ofethanol, the ethanol being a good solvent for lipids and the water beinga good hydrophilic carrier to enable the solution to penetrate moredeeply into the bone particles. The aqueous ethanol solution alsodisinfects the bone by killing vegetative microorganisms and viruses.Ordinarily, at least about 10 to 40 percent by weight of water (i.e.,about 60 to 90 weight percent of defatting agent such as alcohol) ispresent in the defatting disinfecting solution to produce optimal lipidremoval and disinfection within the shortest period of time. A suitableconcentration range of the defatting solution is from about 60 to about85 weight percent alcohol. In one embodiment, the defatting solution hasa concentration of about 70 weight percent alcohol.

In some embodiments, the demineralized bone comprises surfacedemineralized bone. Surface demineralization of bone to a depth justsufficient to expose the osteons provides bone having improvedbiological response while maintaining a mineralized core portion capableof sustaining mechanical loads. Depth of demineralization may be definedby size of the particle, amount of time the particle is in acidsolution, concentration of the acid solution, volume of the acidsolution, and/or temperature of the acid solution, and physical forcesapplied to the bone.

In some embodiments, the bone may be surface demineralized. The surfacemay be an inner surface, such as inside trabeculae or inside a Haversiancanal. In other embodiments the surface may be an outer surface. In someembodiments, surface demineralized refers to the bone comprising atleast one outer surface, or zone of an outer surface, that isdemineralized and possessing a non-demineralized core. In someembodiments, the entirety of the surface may be partially demineralized.In other embodiments, a portion of the surface may be demineralized,such as by exposing only a portion of a particle to the demineralizationprocess, by exposing a portion of the surface to a greater or lesserextent of the demineralization process, by masking, etc.Demineralization may be done to a certain percentage. In someembodiments, that percentage relates to weight percentage. In otherembodiments, that percentage relates to percentage of the size of thebone being demineralized, or to the depth of demineralization. The depthof demineralization of the at least one outer surface thus may be viewedas a percentage of the size of the bone being demineralized or may beviewed as an absolute number.

Demineralization thus may be carried out to a percentage depth of thesize of the bone being demineralized. FIGS. 4 a and 4 b illustratesurface demineralized bone particles. The bone particle 100 of FIG. 4 ais substantially spherical. The bone particle 110 of FIG. 4 b issomewhat elongate.

As shown, the bone particle 100 of FIG. 4 a has a demineralized surfaceregion 106 and a non-demineralized core 108. The bone particle 100includes a length 102 along its longest dimension and a length 104 alongits shortest dimension. The length 102 in the longest dimensioncomprises first and second demineralized portions 103 a and 103 b and anondemineralized portion 105. A percentage of demineralization in thelongest dimension may be determined by summing the length of the firstand second demineralized portions 103 a and 103 b and dividing thattotal by the length 102 (comprising 103 a, 103 b and 105). The length104 in the shortest dimension likewise comprises first and seconddemineralized portions 107 a and 107 b and a nondemineralized portion109. A percentage of demineralization in the shortest dimension may bedetermined by summing the length of the first and second demineralizedportions 107 a and 107 b and dividing that total by the length 104(comprising 107 a, 107 b and 109). A total percentage demineralizationmay be determined by averaging the percent demineralization in thelongest dimension with the percent demineralization in the shortestdimension.

As shown, the bone particle 110 of FIG. 4 b has a demineralized surfaceregion 116 and a non-demineralized core 118. The bone particle 110includes a length 112 along its longest dimension and a length 114 alongits shortest dimension. The longest dimension and shortest dimension aretaken as those measuring largest and smallest, respectively, such as bya micrometer or using other by suitable manner and generally goingthrough the center of the bone particle 110. The length 112 in thelongest dimension comprises first and second demineralized portions 113a and 113 b and a nondemineralized portion 115. A percentage ofdemineralization in the longest dimension may be determined by summingthe length of the first and second demineralized portions 113 a and 113b and dividing that total by the length 112 (comprising 113 a, 113 b,and 115). The length 114 in the shortest dimension likewise comprisesfirst and second demineralized portions 117 a and 117 b and anondemineralized portion 119. A percentage of demineralization in theshortest dimension may be determined by summing the length of the firstand second demineralized portions 117 a and 117 b and dividing thattotal by the length 114 (comprising 117 a, 117 b, and 119). A totalpercentage demineralization may be determined by averaging the percentdemineralization in the longest dimension with the percentdemineralization in the shortest dimension.

Alternatively, percentage demineralization may be based on weightpercent demineralized of total weight of the bone particle.

In some embodiments, demineralization may be carried out to a depth of,for example, at least about 100 microns. Surface demineralization mayalternatively be done to a depth less than or more than about 100microns. Generally, surface demineralization may be done to a depth ofat least 50 microns, at least 100 microns, at least 200 microns, orother. Accordingly, in some embodiments, the demineralized bonecomprises at least one outer surface possessing at least onedemineralized zone and a non-demineralized core, wherein thedemineralized zone of the outer surface of the bone may be, for example,at least about 100 microns thick. The demineralized zone mayalternatively be less than or more than about 100 microns thick. Thedemineralized zone of the surface of the bone is osteoinductive, andtherefore promotes rapid new ingrowth of native host bone tissue into anosteoimplant comprising surface demineralized bone. The osteoimplant maycomprise surface demineralized monolithic bone or an aggregate ofsurface demineralized bone particles, and may be substantially solid,flowable, or moldable. The demineralized zone of the surface of the bonecan be any surface portion.

When it is desirable to provide an osteoimplant having improvedbiological properties while still substantially maintaining the strengthpresent in the osteoimplant prior to demineralization, for example wheremonolithic bone is used, the extent and regions of demineralization ofthe monolithic bone may be controlled. For example, depth ofdemineralization may range from at least about 100 microns to up toabout 7000 microns or more, depending on the intended application andgraft site. In some embodiments, the depth of demineralization isbetween 100 to about 5000 microns, between about 150 to about 2000microns, or between about 200 microns to about 1000 microns. Inalternative embodiments, depth of demineralization may be less thanabout 100 microns. Reference is made to U.S. Pat. No. 7,179,299, hereinincorporated by reference for discussion of surface demineralization.

A benefit of surface demineralized bone is that the demineralizedzone(s) can elastically yield under applied force while the mineralizedcore has strength and load bearing capacity exceeding that ofdemineralized bone. Thus, when the surface demineralized bone issubjected to an applied load, the demineralized zones can conform tocontours of adjacent bone tissue and thereby minimize voids or spacesbetween the osteoimplant and adjacent bone tissue. This can be usefulbecause host bone tissue will not grow to bridge large voids or spaces.Thus, by conforming to the contours of adjacent bone tissue, anosteoimplant comprising surface demineralized monolithic bone exhibitsenhanced biological properties such as, for example, incorporation andremodeling. The non-demineralized inner core imparts mechanical strengthand allows the monolithic osteoimplant to bear loads in vivo. Othernon-demineralized zones provide improved tolerances when engaged withother objects such as, for example, insertion instruments, otherimplants or implant devices, etc. It is noted that some of thesecharacteristics may also be exhibited by an osteoimplant comprising anaggregate of surface-demineralized bone particles.

In one embodiment, an osteoinductive composition comprising partiallydemineralized (or surface demineralized) bone particles is provided. Thepartially demineralized bone particles may, for example, range in sizefrom 500 μm to 4 mm. In one embodiment 10-80 percent of the mineral ofthe mineral content of the bone is removed. When comprised of partiallydemineralized bone particles, the osteoinductive composition has arelatively large demineralized surface area relative to volume. Theparticulation further increases the rate of remodeling of theosteoinductive composition.

Mixtures of one or more types of demineralized bone-derived elements canbe employed. Moreover, one or more of types of demineralizedbone-derived elements can be employed in combination withnon-demineralized bone-derived elements, i.e., bone-derived elementsthat have not been subjected to a demineralization process. Thus, e.g.,the weight ratio of non-demineralized to demineralized (including fullydemineralized, partially demineralized, and surface demineralized) boneelements can broadly range from less than 0:1 to about 0:1 to aboutapproaching 1:0 or greater. Further, in some embodiments, mixtures ofdifferent types of bone-derived elements and different levels ofdemineralization—for example surface demineralized bone chips orparticles and fully demineralized pressed bone fibers, describedbelow—may be used. Suitable amounts can be readily determined by thoseskilled in the art on a case-by-case basis by routine experimentation.

As discussed, the bone may be ground or otherwise processed intoparticles of an appropriate size before or after demineralization. Forpreparing surface demineralized bone particles, the bone is particulatedand then surface demineralized. In certain embodiments, the particlesize is greater than 75 microns, for example ranging from about 100 toabout 3000 microns, or from about 200 to about 2000 or up to greaterthan 10,000 microns. In some embodiments, the particle size may be belowabout 2.8 mm diameter, or may be between about 2.8 and about 4.0 mmdiameter. After grinding the bone, the mixture may be sieved to selectthose particles of a desired size. In certain embodiments, the boneparticles may be sieved though a 50 micron sieve, a 75 micron sieve, andor a 100 micron sieve.

Alternatively, or additionally, the bone may be particulated to formelongate particles or fibers. The bone may be particulated in anysuitable manner, such as by milling or pressing. The bone fibers maycomprise threads or filaments having a median length to median thicknessratio of at least about 10:1 and up to about 500:1, a median length offrom about 2 mm to about 400 mm, a medium width of about 2 mm to about 5mm, and a median thickness of from about 0.02 mm to about 2 mm. Anosteoinductive composition comprising bone fibers tends to more readilyretain its shape due, it would appear, to the tendency of the boneparticles to become entangled with each other. The ability of theosteoinductive composition to maintain its cohesiveness and to resisterosion subsequent to being applied to an osseus defect site isadvantageous since it enhances utilization of the available boneparticles. Bone fibers whose median length to median thickness ratio isat least about 10:1 can be readily obtained by any one of severalmethods, e.g., shaving the surface of an entire bone or relatively largesection of bone. Another procedure for obtaining the bone fibers, usefulfor pieces of bone of up to about 100 mm in length, is the Cortical BoneShredding Mill available from Os Processing Inc., 3303 Carnegie Avenue,Cleveland, Ohio 44115. Reference is made to U.S. Pat. Nos. 5,314,476,5,510,396, 5,507,813, and 7,323,193 herein incorporated by reference fordiscussion of bone fibers.

After demineralization, water optionally may be removed from the boneparticles [block 37 of FIG. 2] and sterilized [block 39 of FIG. 2].Drying may comprise lyophilization, critical point drying, vacuumdrying, solvent dying, or other drying technique. Removing water fromthe particles may be referred to as drying the particles or dehydratingthe particles and may be done to any suitable level. For example, insome embodiments 70% of the water in the bone is removed, 80% of thewater in the bone is removed, 90% of the water in the bone is removed,90% of the water in the bone is removed, 95% of the water in the bone isremoved, or 98% or more of the water in the bone is removed.

Sterilization may be done in any suitable manner. In one embodiment,sterilization may comprise heat sterilizing the bone withoutsubstantially degrading biological properties of the tissue. In someembodiments, sterilization comprises gentle heating of the bone. Inanother embodiment, sterilization comprises heating the bone in theabsence of oxygen. In a further embodiment, sterilization comprisesheating the tissue in the presence of supercritical CO₂. U.S. patentapplication Ser. No. ______ to Method of Treating Tissue, filed Jun. 16,2008, discloses methods of sterilization suitable for use with thepresent invention and is herein incorporated by reference for thepurposes of all that is disclosed therein.

In some embodiments, the demineralized bone may further be treated, forexample to at least partially remove antigens.

IV. Treat the Bone

In accordance with some embodiments, the demineralized bone may betreated such that the collagen structure of the bone is disrupted, shownat block 16 of FIG. 1. Disruption may be done in any suitable mannerincluding, for example, heat treatment, chemical treatment, mechanicaltreatment, energy treatment (e.g., x-ray or radiation), and others. Thecollagen structure of bone comprises a triple helix form. The bone maybe treated such that the triple helix form unwinds but covalentcrosslinks of the structure remain intact. In general, the treatment issuch that the collagen in the bone is denatured or digested to the pointwhere protease enzymes can readily attack it, while at the same timeavoiding the creation of toxic byproducts, and maintaining some of theoriginal strength of the bone. Cortical bone treated as provided hereingenerally remodel faster than untreated cortical bone, and retainstrength in excess of that of cancellous bone.

More specifically, collagen consists of fibrils composed of laterallyaggregated, polarized tropocollagen molecules (MW 300,000). Eachtropocollagen unit consists of three helically wound polypeptideα-chains around a single axis. The strands have repetitive glycineresidues at every third position and numerous proline and hydroxyprolineresidues, with the particular amino acid sequence being characteristicof the tissue of origin. Tropocollagen units combine uniformly to createan axially repeating periodicity. Cross linkages continue to develop andcollagen becomes progressively more insoluble and resistant to lysis onaging. Gelatin results when soluble tropocollagen is denatured, forexample on mild heating, and the polypeptide chains become randomlydispersed. In this state the strands may readily be cleaved by a widevariety of proteases.

Various methods for disrupting the collagen structure of thedemineralized bone may be used. For example, heat treatment, treatmentwith collagenase, other chemical treatment, mechanical treatment, orenergy treatment may be employed. For the purposes of illustration,discussion is made of treating the bone after it has been particulatedand demineralized. It is to be understood that the order ofparticulation, demineralization, and treatment may be varied. U.S.patent application Ser. No. ______, for Osteoinductive DemineralizedCancellous Bone, filed Jun. 16, 2008, is herein incorporated byreference in its entirety for the purposes of all that is disclosedtherein.

Heat Treatment

In embodiments wherein treating the bone comprises heat treatment of thebone, the heat treatment may comprise, for example, gentle heating ofthe bone. In other embodiments, the heat treatment may comprise hightemperature heating of the bone, heating the bone in the absence ofoxygen, or heating the bone in the presence of supercritical fluids suchas CO₂. Generally, any suitable form of heat treatment may be used.

Treatment of the partially demineralized bone may comprise heating thebone to temperatures ranging from approximately 40° C. to approximately120° C. for period of time ranging from approximately 1 minute toapproximately 96 hours. Heating may be done with the partiallydemineralized bone in a dry state, in distilled water, in a neutralbuffer solution, or other. The osteoinductive composition may exhibitthe ability to induce the formation of heterotopic bone in a higherorder animal such as a dog, human, or sheep. In some embodiments, theosteoinductive composition may be combined with osteoinductive growthfactors extracted from bone, recovered from acid used to demineralizedbone, or other.

Thus, in a first embodiment, gentle heating of the bone is performed todisrupt the collagen structure of the bone. Such gentle heatingdenatures proteins in the bone. Heating may be performed, for example,at temperatures of approximately 60 to 70° C. Gentle heating generallydoes not chemically degrade the proteins in the bone. Gentle heatinglimits potential inflammatory response. In another embodiment, the bonemay be defatted before the heat treatment to remove lipids, which are apotential thermal peroxygen compound source. Further, in someembodiments, water may be removed from the bone before heating (as atblock 39 of FIG. 2).

In another embodiment, the bone is heated in the absence of oxygen.Heating in the absence of oxygen may be done in any suitable manner. Forexample, heating may be done using an inert atmosphere, a reducingatmosphere, a vacuum, a shielding coating (providing the coating overthe tissue being done during preparation of the tissue), or other means.Heating cortical bone in the absence of oxygen produces a fasterremodeling cortical bone when implanted in a vertebrate species, with astrength at least equal to that of cancellous bone. Generally, corticalbone so treated possesses at least 30% of its original strength. In someembodiments, the heating conditions may be selected such that they willresult in virally inactivated bone tissue. For example, the bone may beheated at temperatures of approximately 100 to 250° C.

In some embodiments of heating in the absence of oxygen, the bone isheated in an inert atmosphere or in a reducing atmosphere. Suchatmosphere acts as a protective atmosphere. Inert atmospheres mayinclude argon, nitrogen, helium, CO₂ (including supercritical CO₂), ahydrocarbon vapor, mixtures of these gases, etc. Reducing atmospheresmay comprise pure hydrogen or hydrogen mixed with an inert gas whereinthe atmosphere comprises between 1 and 99 percent hydrogen. Using areducing gas, reductive free radicals, for example from hydrogen, areproduced to protect against the effects of oxidative free radicals. Invarious embodiments, the bone may be treated in a chamber wherein theprotective atmosphere is introduced to the chamber and released aftertreatment. The method of release of the atmosphere may be controlled toaffect the bone. For example, slow release of the atmosphere has littleeffect on the bone. In contrast, fast release of the atmosphere maycause the bone to expand and develop pores.

A further embodiment of heating in the absence of oxygen comprisescoating the bone with a protective thermal coating. The protectivethermal coating forms an oxygen barrier and, thus, the bone with theprotective thermal coating may be heated in an oxygenated atmosphere.Such protective thermal coating may comprise, for example, a polymer orwax that does not react with the tissue and that forms an oxygenbarrier. In one embodiment, the protective coating comprises PolyDTEpolymer. In another embodiment, the protective coating comprises a mixof Poly(lactide-co-glycolide) and Poly(ethylene glycol). The protectivecoating may be layered over a monolithic piece of bone or may be mixedwith smaller bone elements—such as particulated bone. When mixed withparticulated bone, for example, the polymer/bone mix may be molded toform an implant.

In some embodiments, the bone is surface demineralized and thenincubated in a phosphate buffer. The demineralized surface of the boneremains osteoinductive. The surface-demineralized bone may then beheated without addition of enzyme inhibitors (sodium azide and iodaceticacid).

Reference is made to U.S. patent application Ser. No. ______, entitled“Osteoinductive Demineralized Cancellous Bone”, filed Jun. 16, 2008, andto U.S. patent application Ser. No. ______ “Method of Treating Tissue”,filed Jun. 16, 2008, both herein incorporated by reference fordiscussion of disrupting the collagen structure of bone.

Chemical Treatment

In accordance with other embodiments, treating the bone to degrade thecollagen structure of the bone comprises treating the bone with achemical. In some embodiments, a chemical may be used to cleavesimultaneously across all three chains of the collagen helix or toattack a single strand of the collagen helix. In some embodiments, thechemical cleaves Type I collagen, e.g., degrades the helical regions innative collagen, preferentially at the Y-Gly bond in the sequencePro-Y-Gly-Pro-, where Y is most frequently a neutral amino acid. Thiscleavage yields products susceptible to further peptidase digestion. Anychemical or protease having one or more of these activities may be usedto treat the demineralized bone.

In one embodiment, the bone is treated with a collagenase enzyme.Generally, when bone is treated with collagenase, natural degradationproducts are formed. Because the dense structure of the bone thatinhibits remodeling may complicate an enzyme treatment process, gettingthe enzyme to penetrate the bone can be difficult. Physical methods suchas centrifugation in an enzyme solution, or the use of a solvent such asDMSO, may thus be used.

Collagenases and their activity on collagens of various types have beenextensively studied. A number of collagenase preparations are availablefrom Worthington Biochemical Corporation, Lakewood, N.J. In general, avariety of different collagenases known in the art can be used todisrupt the collagen structure of the bone. Collagenases are classifiedin section 3.4.24 under the International Union of Biochemistry andMolecular Biology (NC-IUBMB) enzyme nomenclature recommendations (see,e.g., 3.4.24.3, 3.4.24.7, 3.4.24.19). The collagenase can be ofeukaryotic (e.g., mammalian) or prokaryotic (bacterial) origin.Bacterial enzymes differ from mammalian collagenases in that they attackmany sites along the helix.

It will be appreciated that crude collagenase preparations contain notonly several collagenases, but also a sulfhydryl protease, clostripain,a trypsin-like enzyme, and an aminopeptidase. This combination ofcollagenolytic and proteolytic activities is effective at breaking downintercellular matrices, an essential part of tissue disassociation.Crude collagenase is inhibited by metal chelating agents such ascysteine, EDTA, or o-phenanthroline, but not DFP. It is also inhibitedby α2-macroglobulin, a large plasma glycoprotein. Ca²+ is required forenzyme activity. Therefore, it may be desirable to avoid collagenaseinhibiting agents when treating bone matrix with collagenase. Inaddition, although the additional proteases present in some collagenasepreparations may aid in breaking down tissue, they may also causedegradation of desired matrix constituents such as growth factors.Therefore, a purified collagenase that contains minimal secondaryproteolytic activities along with high collagenase activity may be used.For example, a suitable collagenase preparation may contain at least90%, at least 95%, at least 98%, or at least 99% collagenase by weight.The preparation may be essentially free of bacterial components,particularly bacterial components that could cause inflammatory orimmunological reactions in a host, such as endotoxin,lipopolysaccharide, etc. Preparations having a purity greater than 99.5%can also be used. A suitable preparation is chromatographically purifiedCLSPA collagenase from Worthington Biochemical Corporation. Variousprotease inhibitors may be included that do not inhibit collagenase butthat inhibit various proteases that digest BMP. For example, proteaseinhibitors that are known to protect BMP activity from degradationinclude N-ethyl maleimide, benzamidine hydrochloride, iodoacetic acid,PMSF, AEBSF, E-64. Bestatin may also be used, particularly if thepreparation contains aminopeptidase activity. Any of these proteaseinhibitors (or others) may be provided in a composition that is used totreat the demineralized bone.

Bone morphogenetic protein I (BMP-1) is a collagenolytic protein thathas also been shown to cleave chordin (an inhibitor of BMP-2 and BMP-4).Thus, BMP-1 may be of use to alter the physical structure of thedemineralized bone (e.g., by breaking down collagen) and/or to cleavespecific inhibitory protein(s), e.g., chordin or noggin. Proteinsrelated to any of the proteases described herein, i.e., proteins orprotein fragments having the same cleavage specificity, can also beused. It will be appreciated that variants having substantial sequenceidentity to naturally occurring protease can be used. For example,variants at least 80% identical over at least 50%, at least 60%, atleast 70%, at least 80%, at least 90%, or 100% of the length ofnaturally occurring protease (or any known active fragment thereof thatretains cleavage specificity) when aligned for maximum identity allowinggaps can be used.

Collagen can also be broken down by treatment with a strong base, suchas sodium hydroxide. Thus, in some embodiments, sodium hydroxide can beintroduced to the bone to disrupt the collagen structure of the bone.Such introduction may be in the form of a solution with penetrationaided by a centrifuge and/or the addition of DMSO, as is the case for anenzyme. The base will not harm the mineral component of bone; so much ofthe strength (especially compressive strength) is maintained.

Other chemicals, such as cyanogen bromide, may alternatively be used toalter the collagen structure of the bone.

Combinations of treatments designed to degrade collagen can be used; forexample, a mild heating combined with an enzyme or base treatment; or anenzyme treatment followed by a radiation treatment. Any suitablecombination of treatments, including treatments not discussed herein,may be used.

In some embodiments, the partially demineralized bone, whether providedas an aggregate of particles or a monolithic bone, may be compressed toincrease its density. The structure of cancellous bone is less densethan that of cortical bone. By compressing the structure of thecancellous bone, the osteoinductive potential is increased. Compressionmay be done before or after addition of an extract and/or carrier to thepartially demineralized bone. Compression may be achieved via anysuitable mechanism. For example, compression may be achieved bymechanical means, heat, or chemical modification of the collagenousstructure. Reference is made to U.S. patent application Ser. No.11/764,026, entitled “Osteoinductive Demineralized Cancellous Bone”,filed Jun. 15, 2007, herein incorporated by reference for discussion oftechniques for compressing the partially demineralized bone.

V. Add Demineralized Bone Matrix

In some embodiments, demineralized bone matrix (DBM) may be added to thepartially demineralized bone particles. The DBM may comprise monolithicbone, bone particles, bone fibers, or other composition of bone. Anysuitable manner may be used to add the demineralized bone matrix to thepartially demineralized bone particles. Any suitable ratio ofdemineralized bone matrix to partially demineralized bone particles mayresult. The various processing steps set forth herein may be performedin any suitable sequence that provides the desired results. For example,in some embodiments, the at least partially demineralized bone particlesare processed, for example dried, and the demineralized bone matrix isprocessed, for example dried, separately from the partiallydemineralized bone particles. In these embodiments, the at leastpartially demineralized particles and the demineralized bone matrix arecombined after processing. In other embodiments, the partiallydemineralized bone particles and the demineralized bone matrix may becombined and then processed, for example, dried, together. Other stepsalso may be performed in different orders, combined, or omitted, withinthe spirit of the present invention.

In one embodiment, the DBM comprises pressed DBM fibers. Pressed DBMfibers may comprise elongate bone particles. The elongate bone particlesor bone fibers may comprise threads or filaments having a median lengthto median thickness ratio of at least about 10:1 and up to about 500:1,a median length of from about 2 mm to about 400 mm, a medium width ofabout 2 mm to about 5 mm, and a median thickness of from about 0.02 mmto about 2 mm. The DBM fibers may be pressed bone fibers.

Pressed bone fibers refers to the manner by which the bone fibers areformed. Generally, forming the bone fibers by pressing the bone, asdescribed below, results in intact bone fibers of longer length thanother methods of producing elongate bone fibers, with the bone fibersretaining more of the native collagen structure. The bone may beparticulated via pressure applied to the bone, as discussed in U.S. Pat.No. 7,323,193.

The entire bone can then be demineralized or can be sectioned beforedemineralization. The entire bone or one or more of its sections issubjected to demineralization to reduce the inorganic content of thebone, e.g., to less than about 10% by weight, less than about 5% byweight, or less than about 1% by weight, residual calcium.Demineralization of the bone can be accomplished in accordance withknown and conventional procedures, as described above.

Following demineralization, the bone is subdivided into demineralizedbone fibers of desired configuration and size. One method suitable forsubdividing demineralized bone stock is to subject the bone to pressing.One pressing technique comprises applying pressure to the unconstraineddemineralized bone. Examples include pressing the bone using a mortarand pestle, applying a rolling/pressing motion such as is generated byone or more rolling pins, or pressing the bone pieces between flat orcurved plates. In other embodiments, flat or any other suitableconfiguration of plate or pressing surface may be used. These flatteningpressures cause the bone fibers to separate. Pressing demineralized bonein this manner provides intact natural bone collagen fibers (as opposedto composite fibers made from joined short fiber sections) that can beas long as the fibers in the demineralized bone stock from which theywere obtained.

Another suitable pressing technique comprises mechanically pressingdemineralized bone which is constrained within a sealed chamber havingat least one aperture in its floor or bottom plate. The separated fibersextrude through the holes with the hole diameter limiting the maximumdiameter of the extruded fibers. As with the unconstrained pressingmethod, this constrained technique results in fibers that are largelyintact (as far as length is concerned) but separated bone collagenbundles.

In a combined unconstrained/constrained pressing technique that resultsin longer fibers by minimizing fiber breakage, the demineralized bone isfirst pressed into an initially separated mass of fibers while in theunconstrained condition and thereafter these fibers are constrainedwithin the sealed chamber where pressing is continued.

In general, pressing of demineralized bone to provide demineralized bonefibers can be carried out at from less than about 1,000 psi, to about1,000 to about 40,000 psi, or from about 5,000 to about 20,000 psi, orgreater than about 40,000 psi.

Depending on the procedure employed, the demineralized bone fibers maycomprise elongate bone fibers with at least about 80 weight percent, atleast about 90 weight percent, or at least about 95 weight percent, ofthe fibers possessing a median length of from about 2 to about 300 mm orgreater, for example, a median length of from about 5 to about 50 mm, amedian thickness of from about 0.5 to about 15 mm, for example, a medianthickness of from about 1 to about 5 mm, a median width of from about 2to about 35 mm, for example, a median width of from about 2 to about 20mm, and a median length to thickness ratio and/or a median length towidth ratio of from about 2 to 200, for example from about 10 to about100. In some embodiments, the mass of bone fibers can be graded orsorted into different sizes, e.g., by screening, and/or any lessdesirable size(s) of bone fibers that may be present can be reduced oreliminated.

The demineralized bone fibers may be dried, for example usinglyophilization, critical point drying, vacuum drying, solvent dying, orother drying technique.

VI. Provide a Tissue-Derived Extract

Returning to FIG. 1, a tissue-derived extract optionally may be added,shown at block 18, to the partially demineralized bone, or, in someembodiments, to the partially demineralized bone and demineralized bonematrix. The extract may be derived from any suitable tissue, such asbone, bladder, kidney, brain, skin, or connective tissue. Further, theextract may be derived in any suitable manner. The extract may beallogenic, autogenic, xenogenic, or transgenic. In embodiments whereinthe extract is bone-derived, the bone may be cortical, cancellous, orcorticocancellous and may be demineralized, partially demineralized, ormineralized. In some embodiments, the extract may comprise demineralizedbone, partially demineralized bone, mineral derived from bone, orcollagen derived from bone. In some embodiments, the tissue-derivedextract may be a protein extract.

As previously discussed, in the art, demineralized bone is oftenparticulated. Typically, such particulation comprises sieving theparticles to select only particles having at least a certain size.Particles below that size fall through the sieve and are categorized aswaste particles. In accordance with some embodiments, the extract isderived from such waste particles.

DBM preparations have been used for many years in orthopedic medicine topromote the formation of bone. For example, DBM has found use in therepair of fractures, in the fusion of vertebrae, in joint replacementsurgery, and in treating bone destruction due to underlying disease suchas rheumatoid arthritis. DBM is thought to promote bone formation invivo by osteoconductive and osteoinductive processes. The osteoinductiveeffect of implanted DBM compositions is thought to result from thepresence of active growth factors present on the isolated collagen-basedmatrix.

A simple and economically viable method for extracting osteoinductivefactors from bone is provided herein. It is to be appreciated that thismethod may be applied to other tissues. The method comprises extractingosteoinductive factors such as noncollagenous proteins (includingosteogenic growth factors) from DBM using a chaotropic solvent or adetergent. The chaotropic solvent may be guanidine hydrochloride of anysuitable concentration, such as 4M. The detergent may be sodiumdodecylsulfate in any suitable concentration, such as 1%. The chemicalused for extraction is removed in an efficient manner that preserves thebiological activity of the growth factors. The biologically activecomponents are concentrated by purifying away nonessential proteins andinhibitors of bone morphogenetic protein, and the protein extracts arethen combined with a biologically compatible delivery vehicle.

Using the method described, the extraction process is optimized by usingrelatively low cost chaotropic agents, and relatively easy-to-removedetergents. Methods to increase the speed of renaturing the extractedproteins are further provided. Typically in the art, dialysis againstwater is used to remove the detergent or chaotropic agent. However, byprecipitating the proteins with ethanol, acetone, ammonium sulfate, orpolyethylene glycol, dialysis against water is not necessary. Further,ultrafiltration may be used, thereby also avoiding dialysis.

Generally, extracted osteoinductive factors have lower specific boneforming activity when compared to the starting material (e.g., thetissue from which the osteoinductive factors are extracted). This may becaused by protein denaturation that results from extraction. Forexample, when guanidine is used to extract hydrophobic osteoinductiveproteins, the proteins lose their native three-dimensional conformation.As a result, unless they regain their normal shape upon removal of theguanidine, they no longer are active. The addition of chemicalchaperones to the guanidine solution may prevent this proteindenaturation. Suitable chemical chaperones include glycerol, trehalose,proline, glycine betaine, and dextrose, along with mixtures of these andothers. These chemical chaperones enable the osteoinductive proteins toregain their native three-dimensional conformation when the guanidine isremoved. They also substantially prevent protein denaturation duringlyophilization.

A method for extracting osteoinductive factors from the mineralcomponent of bone is provided to recover growth factor activity that isnormally lost during the demineralization process. It is known that 4 Mguanidine hydrochloride can extract osteoinductive factors from finelypowdered mineralized bone. Additionally, osteoinductive factors can berecovered from the acid that is typically used to demineralized bone.These osteoinductive factors are normally lost during thedemineralization process and treated as waste.

In some embodiments, the tissue-derived extract to be added to thepartially demineralized bone may be derived from the acid used todemineralize bone. Growth factors may be extracted from the mineralphase of bone using, for example, the following procedure. As previouslydescribed, bone is at least partially demineralized. The bone maycomprise powder, fibers, chips, or other. The bone may be demineralizedin an acid, for example 1M citric acid, 2M citric acid, or 0.6N HCl, attemperatures ranging from, for example 1° C. to 28° C. for time periodof, for example 10 minutes to 96 hours. In one embodiment, the bone isdemineralized in an acid at a temperature of 4° C. Afterdemineralization, the acid used for demineralization contains growthfactors and mineral. The acid may be dialyzed against water to cause themineral phase and the protein growth factors to co-precipitate. Thisbiphasic (protein and mineral) material may then be collected byfiltration or centrifugation and combined with a carrier or lyophilized.

In alternative embodiments, the protein and mineral material in the acidmay be separated by dialyzing the acid, also referred to as thedemineralization bath, against a weak acid, for example 0.25M citricacid. In such embodiment, the mineral phase passes through the dialysisbag and the protein phase (collagen fragments, growth factors, etc.) isleft within the bag. The protein phase can then be recovered bydialyzing against water and separating water soluble and water insolubleproteins from one another.

In one embodiment, the method for extracting growth factors comprisesdemineralizing powdered bone with dilute acid within a dialysis bag.Suitable dilute acid includes 0.05 M to 1.0 M HCl and 1M or 2M citricacid. After removing the demineralized bone, the contents of the bag maybe further dialyzed against dilute acid to remove the mineralcomponents. A volatile acid, such as acetic acid, can be used tofacilitate recovery by lyophilization.

Proteases may reduce the activity of the osteoinductive factors indemineralized bone by breaking down those osteoinductive factors. Thisnegative effect may be reduced or eliminated by adding proteaseinhibitors to the HCl solution. Suitable protease inhibitors includeN-ethyl maleimide, benzamidine HCl, cysteine, or iodoacetic acid.Alternatively, the bone may be heated briefly to inactivate theproteases, which are relatively more heat sensitive than the growthfactors. A suitable heating regimen is 5 minutes at 60° C., or 1 minuteat 90° C.

Thus, mineralized bone or bone mineral recovered from demineralizationacid may be used for purifying recovered proteins. The protein phaserecovered from the demineralization bath may be solubilized in urea orother form of detergent solution. The bone stimulating growth factorsmay then be purified, for example using a hydroxyapatite affinitychromatography scheme.

In one embodiment the tissue derived extract may comprise a proteincomposition substantially free from inorganic components. The proteincomposition may comprise less than 5% inorganic components by weight. Inan alternative embodiment, a protein composition comprising organiccomponents ranging from approximately 6% to approximately 20% by weightis provided. In another embodiment, a protein composition comprisingorganic components ranging from approximately 21% to approximately 50%may be provided. In yet a further embodiment, a protein compositioncomprising organic components ranging from approximately 51% toapproximately 90% may be provided. The protein composition may berecovered from acid used to demineralize bone. The protein compositionmay alternatively be extracted from other tissues or in other manners.The proteinaceous material of the protein composition may be purified bychromatography, electrophoresis, or other chemical or physical means.The protein composition may be combined with another material such asdemineralized bone, hydroxyapatite, tricalcium phosphate (TCP),dicalcium phosphate (DCP), or other. In some embodiments, the proteincomposition may exhibit the ability to induce heterotopic bone formationin an athymic animal. In some embodiments the protein composition canserve as a source of collagen Type I, collagen Type I residues, andother extracellular matrix proteins that can support tissue repairprocesses such as angiogenesis, osteoconduction and wound healing. Asthe protein material has desirable handling properties when combinedwith water or glycerol, the protein can also serve as a carrier for avariety of bone forming matrices including partially demineralized orfully demineralized bone matrix.

In some embodiments, the tissue-derived extract may be solubilized in anappropriate medium, such as 6M urea, exposed to hydroxyapatite, TCP,DCP, mineralized bone, surface demineralized bone, or mineral recoveredfrom acid used to demineralize bone. The protein may further bepermitted to adsorb onto mineral surfaces and be washed with a solutioncomprising, for example, sodium phosphate ranging from approximately 1mM to 50 mM in concentration. The proteins may then be eluted with asolution comprising, for example, sodium phosphate ranging inconcentrations from between approximately 100 mM to approximately 500mM.

With specific reference to extracts from bone, proteins in bone matrixtend to be insoluble and may associate with the bone matrix. Generally,collagens are among the most insoluble osteoinductive factors.Extraction methods may be used to increase the solubility of theosteoinductive factors to facilitate extraction of the osteoinductivefactors. Generally, growth factors are hydrophobic and are not readilysoluble. Thus, growth factors may be treated to improve solubility.

The solubility of demineralized bone in one or more solvents (e.g., anaqueous medium) may be changed, e.g., increased, relative, for example,to the solubility of a standard demineralized bone not exposed to thetreatment. Preferably, the aqueous medium is at physiologicalconditions, e.g., pH, osmotic pressure, salt concentration, etc. withinphysiologically appropriate ranges. For example, the pH may beapproximately 7.2-8.0, or preferably 7.4-7.6. The osmotic pressure maybe approximately 250-350 mosm/kg, 280-300 mosm/kg, etc. More generally,the pH may be between approximately 3-11, 4-10, 5-9, 6-8.5, etc. Theosmotic pressure may be between 50-500 mosm/kg, 100-350 mosm/kg, etc.The salt concentration may be approximately 100-300 mM NaCl, e.g.,approximately 150 mM NaCl. The aqueous medium may be tissue culturemedium, blood, extracellular fluid, etc., and the physiologicalconditions may be conditions such as are typically found within thesefluids and/or within a body tissue such as muscle. The solubility may beincreased at any temperature, e.g., room temperature, body temperatureof a subject such as a human or animal, etc.

Collagenase treatment of standard human DBM increases its solubilityrelative to that of untreated standard human DBM. The solubility of theDBM may be increased by exposure to an appropriate treatment orcondition, e.g., collagenase treatment, radiation, heat, etc. The extentto which the solubility is increased may be varied by varying the natureof the treatment (e.g., the enzyme concentration) and/or the time overwhich it is applied. A combination of treatments may be used. In certainembodiments, the solubility of the DBM composition is greater than thatof a standard DBM composition by between 10% and 4000% percent. Forexample, the solubility may be greater by between 10% and 100%, 100% and500%, 500% and 1000%, 1000% and 2000%, 2000% and 3000%, 3000% and 4000%or any other range between 10% and 4000%. The solubility may be assessedat any time following the treatment to increase the solubility of theDBM composition. For example, the DBM may be placed in aqueous mediumfor a period of time such as 24-48 hours, 3, 4, 5, 6, or 7 days, 10days, 14 days, etc. The amount of DBM remaining after the period of timeis quantitated (e.g., dry weight is measured) and compared with theamount that was present initially. The extent to which the amountdecreases after a period of time serves as an indicator of the extent ofsolubilization.

In alternative embodiments, tissue-derived extracts may be derived inany suitable manner. Further, during extraction, coprecipitates may beused. Thus, for example, using bone, the bone may be treated with achaotropic solvent such as guanidine hydrochloride. The bone andchaotropic solvent are dialyzed against water. As the chaotropic solventdecreases, it is replaced by water. Precipitates are then extracted.Coprecipitates, such as protein, collagen, collagen fragments, albumen,or protein with RGD sequences, may be extracted. The extractedosteoinductive factors and coprecipitates may then be blended into ahomogenous mixture.

In one embodiment, a simplified extraction process may be used that isamenable to batch processing. K. Behnam, E. Brochmann, and S. Murray;Alkali-urea extraction of demineralized bone matrix removes noggin, aninhibitor of bone morphogenetic proteins; Connect Tissue Res. 2004,45(4-5):257-60.

A number of naturally occurring proteins from bone or recombinantosteoinductive factors have been described in the literature and aresuitable for use in the osteoinductive composition as a tissue-derivedextract. Recombinantly produced osteoinductive factors have beenproduced by several entities. Creative Biomolecules of Hopkinton, Mass.,produces an osteoinductive factor referred to as Osteogenic Protein 1,or OP1. Genetics Institute of Cambridge, Mass., produces a series ofosteoinductive factors referred to as Bone Morphogenetic Proteins 1-13(i.e., BMP 1-13), some of which are described in U.S. Pat. Nos.5,106,748 and 5,658,882 and in PCT Publication No. WO 96/39,170, eachherein incorporated by reference. Purified osteoinductive factors havebeen developed by several entities. Collagen Corporation of Palo Alto,Calif., developed a purified protein mixture that is purported to haveosteogenic activity, as described in U.S. Pat. Nos. 4,774,228,4,774,322, 4,810,691, and 4,843,063, each herein incorporated byreference. Urist developed a purified protein mixture which is purportedto be osteogenic, as described in U.S. Pat. Nos. 4,455,256, 4,619,989,4,761,471, 4,789,732, and 4,795,804, each herein incorporated byreference. International Genetic Engineering, Inc. of Santa Monica,Calif., developed a purified protein mixture that is purported to beosteogenic, as described in U.S. Pat. No. 4,804,744, herein incorporatedby reference.

One osteoinductive factor that may be used as a tissue-derived extractin the osteoinductive composition is described in detail in U.S. Pat.No. 5,290,763, herein incorporated by reference. This osteoinductivefactor has a high osteogenic activity and degree of purity. Theosteoinductive factor of the '763 patent exhibits osteoinductiveactivity at about 3 micrograms when deposited onto a suitable carrierand implanted subcutaneously into a rat. In one embodiment, theosteoinductive factor is an osteoinductively active mixture of proteinsthat exhibit the gel separation profile shown in FIG. 1 of U.S. Pat. No.5,563,124, herein incorporated by reference.

In some embodiments, the tissue-derived extract may comprise bonestimulating growth factors, for example recovered from the mineral phaseof bone. The bone stimulating growth factors may be purified using anapatite affinity chromatography scheme. Thus, mineralized or surfacedemineralized bone may be used as a chromatography resin. Bone mineralcomprises calcium phosphate sales similar to hydroxyapatite. To usemineralized or surface demineralized bone as a chromatography resin,excess lipid and protein may be removed from the surfaces of the bone.In other embodiments, a similar scheme may be done using demineralizedbone matrix as a resin. In yet further embodiments, recovered inorganicbone mineral (sintered or unsintered) may be used as the chromatographyresin.

In one embodiment, the protocol for such scheme may be as follows.Mineralized bone particles, for example ranging from 100 μm to 5 mm, areprepared. The surface of the mineralized bone particles is cleaned, forexample by soaking or stirring the bone particles in a dilute base suchas 0.1M NaOH for several minutes. Generally, such surface cleaningremoves proteins as well as lipids. In alternative embodiments, surfacecleaning may be performed using supercritical CO₂. Growth factorextracts from the mineral phase may be solubilized in a chaotropicsolvent such as 6M urea. The growth factor solution may then be mixedwith the mineralized bone particles, for example, for several minutes.During such mixing, proteins having an affinity for hydroxyapatite bindto the bone surfaces. The bone-protein complex is then precipitated andthe supernatant removed. The bone-protein complex may be treated toremove weakly bound proteins such as collagen fragments while retainingosteoinductive proteins (the osteoinductive proteins remain bound to thematerial). Such treatment may comprise treating the bone-protein complexwith a 6M urea containing low concentrations of sodium phosphate. Thetreated bone-protein complex may be centrifuged and the supernatantaspirated. In some embodiments, the bone-protein complex may be treatedwith urea containing higher concentrations of sodium phosphate (e.g.,100 mM, 180 mM, or 250 mM) to release bound osteoinductive proteins.Alternatively, the bone-osteoinductive protein complex may belyophilized and formulated with a carrier, for example for orthopedicapplications. Further, the bone protein complex may be used as a growthfactor microcarrier that can be distributed in a DBM macrocarrier.

Extraction may extract, for example, both osteoinductive factors andtheir inhibitors. If the inhibitors are extracted, the osteoinductivefactors may be separated out. This may be referred to as removal of theinhibitors or concentration of the osteoinductive factors. As a generalmatter, both the osteoinductive factors and the inhibitors may beextracted and both the osteoinductive factors and the inhibitors may beused for forming the osteoinductive composition. Alternately, only theosteoinductive factors (and not their inhibitors) are extracted and onlythe osteoinductive factors are used for manufacturing the osteogenicosteoimplant. Lastly, both the osteoinductive factors and the inhibitorsmay be extracted and only the osteoinductive factors may be used forforming the osteoinductive composition. In some embodiments, it may bedesirable to remove inhibitors or concentrate the osteoinductivefactors. This is optional and may be done by any suitable method.Generally, it may be desirable to remove the inhibitors quickly withoutdenaturing the osteoinductive factors. Reference is made to U.S. patentapplication Ser. Nos. 11/555,606 and 11/555,608, to which the presentapplication claims priority and which is herein incorporated byreference for discussion of other processing that may be used. Theembodiment of extraction and resultant use of osteoinductive factorswith or without inhibitors is not a limiting feature of the presentinvention.

In some embodiments, the tissue-derived extract may be modified in oneor more ways, e.g., its protein content can be augmented or modified asdescribed in U.S. Pat. Nos. 4,743,259 and 4,902,296, the contents ofwhich are incorporated by reference herein. The extract can be admixedwith one or more optional substances such as binders, fillers, fibers,meshes, substances providing radiopacity, plasticizers,biostatic/biocidal agents, surface active agents, and the like, priorto, during, or after adding to the carrier.

VII. Add Extract to the Partially Demineralized Bone

As shown at block 18 of FIG. 1, the tissue-derived extract may be addedto the partially demineralized bone, or, in some embodiments, to thepartially demineralized bone and demineralized bone matrix. Suchaddition may be done in any suitable manner. As discussed, thetissue-derived extract may comprise extracted osteoinductive factors andpossibly inhibitors. For ease of reference, unless otherwise noted,reference to osteoinductive factors refers to osteoinductive factorswith or without inhibitors.

The tissue-derived extract may be added in any suitable extract dose.Generally the dosage may be from less than 1× to approximately 10×. Forthe purposes of this disclosure, 1× is defined as the amount of extractthat may be derived from a single clinically relevant unit of tissue.For example, using bone as the tissue, for a 10 cc unit of DBM,mineralized bone, or surface demineralized bone, 1× is the amount ofextract that can be derived from 10 cc of the bone.

When the extract is added to the partially demineralized bone, thepartially demineralized bone may first act as a bulking means forapplying a small amount of extracted material. The partiallydemineralized bone also may serve as a scaffold, and may aid incontrolling release kinetics. Any suitable shape, size, and porosity ofpartially demineralized bone may be used. Rat studies show that the newbone is formed essentially having the dimensions of the deviceimplanted. Generally, particle size influences the quantitative responseof new bone; particles between 70 μm and 420 μm elicit the maximumresponse. However, other particle sizes may be used.

The partially demineralized bone may comprise a DBM preparation.Generally, the DBM preparation will include at least some portion ofsurface demineralized bone. DBM prepared by any method may be employed,including particulate or fiber-based preparations, mixtures of fiber andparticulate preparations, fully or partially demineralized preparations,mixtures of fully and partially demineralized preparations, and surfacedemineralized preparations. See U.S. Pat. No. 6,326,018, Reddi et al.,Proc. Natl. Acad. Sci. USA (1972) 69:1601-1605; Lewandrowski et al.,Clin. Ortho. Rel. Res., (1995) 317:254-262; Lewandroski et al., J.Biomed. Mater. Res. (1996) 31:365-372; Lewandrowski et al. CalcifiedTiss. Int., (1997) 61:294-297; Lewandrowski et al., I Ortho. Res. (1997)15:748-756, each of which is incorporated herein by reference. Suitabledemineralized bone matrix compositions are described in U.S. Pat. No.5,507,813, herein incorporated by reference. As discussed, the bone maybe particulated. In alternative embodiments, the bone may be in the formof a section that substantially retains the shape of the original bone(or a portion thereof) from which it was derived. Also useful arepreparations comprising additives or carriers such as polyhydroxycompounds, polysaccharides, glycosaminoglycan proteins, nucleic acids,polymers, poloxamers, resins, clays, calcium salts, and/or derivativesthereof.

As discussed, the tissue-derived extract may be combined with thepartially demineralized bone. The manner by which the tissue-derivedextract is combined with the partially demineralized bone can influencethe biological activity of the final composition. The tissue-derivedextract may be lyophilized, resulting in a powder. In some situations,adding a powder to a bone matrix may be challenging. Thus, it may bedesirable to process a powdered tissue-derived extract to form ahomogenous mixture that may be more easily added to partiallydemineralized bone. This can impact release kinetics of any growthfactors.

Thus, in a specific example, if the tissue-derived extract islyophilized and then added to the partially demineralized bone, thesolution may be inhomogeneous, with most of the tissue-derived extractconcentrated on the outside of the partially demineralized bone. If thetissue-derived extract is added to very thin DBM sheets and each sheetis folded in on itself, the distribution of tissue-derived extract maybe more homogenous. The sheets in such an embodiment can be very thin,on the order of microns. The sheets may comprise, for example, thepartially demineralized bone mixed with a carrier, described more fullybelow.

Any suitable method for adding, or dispersing, the tissue-derivedextract to the partially demineralized bone may be used. Generally, theprocedures used to formulate or disperse the tissue-derived extract ontothe partially demineralized bone are sensitive to the physical andchemical state of both the tissue-derived extract and the partiallydemineralized bone. In some embodiments, the extract may be precipitateddirectly onto the partially demineralized bone.

In one embodiment, the tissue-derived extract is blended with a bulkingagent to form a homogenous mixture. This mixture is added to thepartially demineralized bone. Alternatively, the tissue-derived extractmay be blended with coprecipitates and this blend may be added to thepartially demineralized bone.

In some embodiments, after the extract has been added to the partiallydemineralized bone, the partially demineralized bone may have a BMPcontent (BMP-2 content, BMP-4 content, BMP-7 content, TGF-beta content,IGF-II content, MMP-13 content, and/or aggregate BMP content) of atleast approximately 110% that of demineralized bone without addedtissue-derived extract.

Thus, in some embodiments, an osteoinductive composition comprisingsurface demineralized bone particles and tissue-derived extract isprovided. The tissue-derived extract may be adsorbed to the surfaces ofthe partially demineralized bone particles. Weakly bound components maybe eluted using, for example, low concentrations of sodium phosphate(for example, 5 mM to 50 mM), thereby concentrating the tissue-derivedextract. For extract derived from bone, in some embodiments, analysis ofthe proteins bound to the surfaces of the surface demineralized boneparticles indicates a ratio of Histone H2A to total protein boundelevated by a factor of 2 to 10,000 times over the normal ratio found inextracts of demineralized bone matrix or protein recovered from acidused to demineralize bone. In some embodiments, analysis of the proteinsbound to the surfaces of the surface demineralized bone particlesindicates a ratio of Secreted Phosphoprotein 24 to total protein boundelevated by a factor of 2 to 10,000 times over the normal ratio found inextracts of demineralized bone matrix or protein recovered from acidused to demineralize bone. In some embodiments, analysis of the proteinsbound to the surfaces of the surface demineralized bone particlesindicates a ratio of BMP-2 to total protein bound elevated by a factorof 2 to 10,000 times over the normal ratio found in extracts ofdemineralized bone matrix or protein recovered from acid used todemineralize bone. In some embodiments, analysis of the proteins boundto the surfaces of the surface demineralized bone particles indicates aratio of BMP-4 to total protein bound elevated by a factor of 2 to10,000 times over the normal ratio found in extracts of demineralizedbone matrix or protein recovered from acid used to demineralize bone. Insome embodiments, analysis of the proteins bound to the surfaces of thesurface demineralized bone particles indicates a ratio of TGF-Beta tototal protein bound elevated by a factor of 2 to 10,000 times over thenormal ratio found in extracts of demineralized bone matrix or proteinrecovered from acid used to demineralize bone.

In some embodiments, no tissue-derived extract may be added to thepartially demineralized bone.

VIII. Add Partially Demineralized Bone to Delivery Vehicle

As shown at block 19 of FIG. 1, the partially demineralized bone, withor without a tissue-derived extract and/or demineralized bone matrix,optionally may be used with a delivery vehicle. In one embodiment, suchdelivery vehicle may be a carrier to which the partially demineralizedbone is added [block 20 of FIG. 1]. In another embodiment, such deliveryvehicle may be a covering in which the partially demineralized bone isprovided [block 22 of FIG. 1]. In other embodiments, a carrier and acovering both may be used. The partially demineralized bone and deliveryvehicle together form an osteoimplant useful in clinical applications.

Add Partially Demineralized Bone to Carrier

The carrier may be formulated to impart specific handlingcharacteristics to the composition. For example, in some embodiments,the carrier may be formulated such that the composition substantiallyretains its shape in fluids such as blood, serum, or water. Such carriermay comprise, for example, a combination of alginate and chitosan, anacidic alginate (a combination of alginate and an acid), or other.

Suitable carriers include DBM, including surface demineralized bone;mineralized bone; nondemineralized cancellous scaffolds; demineralizedcancellous scaffolds; cancellous chips; particulate, demineralized,guanidine extracted, species-specific (allogenic) bone; speciallytreated particulate, protein extracted, demineralized, xenogenic bone;collagen; synthetic hydroxyapatites; synthetic calcium phosphatematerials; tricalcium phosphate, sintered hydroxyapatite, settablehydroxyapatite; polylactide polymers; polyglycolide polymers,polylactide-co-glycolide copolymers; tyrosine polycarbonate; calciumsulfate; collagen sheets; settable calcium phosphate; polymeric cements;settable poly vinyl alcohols, polyurethanes; resorbable polymers; andother large polymers; liquid settable polymers; and other biocompatiblesettable materials. The carrier may further comprise a polyol (includingglycerol or other polyhydroxy compound), a polysaccharide (includingstarches), a hydrogel (including alginate, chitosan, dextran, pluronics,N,O-carboxymethylchitosan glucosamine (NOCC)), hydrolyzed cellulose, ora polymer (including polyethylene glycol). In embodiments whereinchitosan is used as a carrier, the chitosan may be dissolved using knownmethods including in water, in mildly acidic aqueous solutions, inacidic solutions, etc. The carrier may further comprise a hydrogel suchas hyaluronic acid, dextran, Pluronic block copolymers of polyethyleneoxide and polypropylene, and others. Suitable polyhydroxy compoundsinclude such classes of compounds as acyclic polyhydric alcohols,non-reducing sugars, sugar alcohols, sugar acids, monosaccharides,disaccharides, water-soluble or water dispersible oligosaccharides,polysaccharides and known derivatives of the foregoing. An examplecarrier comprises glyceryl monolaurate dissolved in glycerol or a 4:1 to1:4 weight mixture of glycerol and propylene glycol. Reference is madeto U.S. Pat. No. 5,314,476 for other carriers including polyhydroxycarriers, to U.S. Pat. No. 6,884,778 for biocompatible macromers thatmay be used as carriers, and to U.S. Patent Publication No. 2003/0152548for cross-linkable monomers that may be used as carriers, all hereinincorporated by reference. Settable materials may be used, and they mayset up either in situ, or prior to implantation. In embodiments wherealginate salt (alginate sodium) is used as a settable carrier, thealginate sodium may be dissolved in water with mild acids. After addingpartially demineralized bone, including surface demineralized bone, areaction may occur between acid in alginate solution and minerals inbone to release calcium ions, which may cross-link alginate to help setthe formulation. Optionally, xenogenic bone powder carriers also may betreated with proteases such as trypsin. Xenogenic carriers may betreated with one or more fibril modifying agents to increase theintraparticle intrusion volume (porosity) and surface area. Usefulagents include solvents such as dichloromethane, trichloroacetic acid,acetonitrile and acids such as trifluoroacetic acid and hydrogenfluoride. The choice of carrier may depend on the desiredcharacteristics of the composition. In some embodiments, a lubricant,such as water, glycerol, or polyethylene glycol may be added.

In some embodiments, the osteoinductive composition may comprise surfacedemineralized bone particles, demineralized bone matrix, tissue-derivedextract such as collagenous extract, and glycerol. The osteoinductivecomposition may be configured to be moldable, extrudable, orsubstantially solid. The osteoinductive composition may be configured tosubstantially retain its shape in water for a period of time.

Any suitable shape, size, and porosity of carrier may be used. In someembodiments, the carrier may be settable and/or injectable. Such carriermay be, for example, a polymeric cement, a settable calcium phosphate, asettable poly vinyl alcohol, a polyurethane, or a liquid settablepolymer. Suitable settable calcium phosphates are disclosed in U.S. Pat.Nos. 5,336,264 and 6,953,594, herein incorporated by reference. Hydrogelcarriers may additionally impart improved spatial properties, such ashandling and packing properties, to the osteoconductive composition. Aninjectable carrier may be desirable where the composition is used with acovering. Generally, the carrier may have several functions. In someembodiments, it carries the tissue-derived extract and partiallydemineralized bone and allows appropriate release kinetics. The carriermay also accommodate each step of the cellular response during bonedevelopment, and in some cases protect the tissue-derived extract fromnonspecific proteolysis. In addition, selected materials must bebiocompatible in vivo and optionally biodegradable. In some uses, thecarrier acts as a temporary scaffold until replaced by new bone.Polylactic acid (PLA), polyglycolic acid (PGA), and various combinationshave different dissolution rates in vivo. In bone, the dissolution ratescan vary according to whether the composition is placed in cortical ortrabecular bone.

The carrier may comprise a shape-retaining solid made of loosely adheredparticulate material, e.g., with collagen. It may alternatively comprisea molded, porous solid, a monolithic solid, or an aggregate ofclose-packed particles held in place by surrounding tissue. Masticatedmuscle or other tissue may also be used. Large allogenic bone implantsmay act as a carrier, for example where their marrow cavities arecleaned and packed with particles and the osteoinductive factors.

In one embodiment, the osteoinductive composition induces endochondralbone formation reliably and reproducibly in a mammalian body. Thecarrier may comprise particles of porous materials. The pores may be ofa dimension to permit progenitor cell migration into the carrier andsubsequent differentiation and proliferation. The particle size thus maybe within the range of approximately 70 μm to approximately 850 μm, from70 μm to approximately 420 μm, or from approximately 150 μm toapproximately 420 μm. It may be fabricated by close packing particulatematerial into a shape spanning the bone defect, or by otherwisestructuring as desired a material that is biocompatible, and preferablybiodegradable in vivo to serve as a “temporary scaffold” and substratumfor recruitment of migratory progenitor cells, and as a base for theirsubsequent anchoring and proliferation. For such embodiments, usefulcarrier materials include collagen; homopolymers or copolymers ofglycolic acid, lactic acid, and butyric acid, including derivativesthereof; and ceramics, such as hydroxyapatite, tricalcium phosphate andother calcium phosphates. Combinations of these carrier materials alsomay be used.

One way to protect small size particles from cellular ingestion and/orto provide a diffusion barrier is to embed them in a monolithicbioabsorbable matrix, and then fragment the particle-containingmonolithic matrix into particle sizes greater than 70 microns, forexample, greater than 100 microns, or greater than 150 microns in theirsmallest dimension. Suitable matrices for embedding small partiallydemineralized particles include biocompatible polymers and settingcalcium phosphate cements. Generally the particulate partiallydemineralized bone/polymer weight ratio will range from about 1:5 toabout 1:3. In the case of calcium phosphate, the partially demineralizedbone will be present up to 75% by weight. Particulation of a monolithcan be accomplished by conventional milling or grinding, or through theuse of cryomilling, or freezing followed by pulverization. In oneembodiment, partially demineralized bone particles are embedded in aresorbable polymer. In a further embodiment, partially demineralizedbone particles are embedded in one of the setting calcium phosphatesknown to the art.

The carrier may comprise a number of materials in combination, some orall of which may be in the form of fibers and/or particles. The carriermay comprise calcium phosphates. Driessens et al. “Calcium phosphatebone cements,” Wise, D. L., Ed., Encyclopedic Handbook of Biomaterialsand Bioengineering, Part B, Applications New York: Marcel Decker;Elliott, Structure and Chemistry of the Apatites and Other CalciumPhosphates Elsevier, Amsterdam, 1994, each of which is hereinincorporated by reference. Calcium phosphate matrices include, but arenot limited to, dicalcium phosphate dihydrate, monetite, tricalciumphosphate, tetracalcium phosphate, hydroxyapatite, nanocrystallinehydroxyapatite, poorly crystalline hydroxyapatite, substitutedhydroxyapatite, and calcium deficient hydroxyapatites.

In one embodiment, the carrier comprises an osteoinductive material suchas a mineralized particulated material, osteoinductive growth factors,or partially demineralized bone. The mineralized particulated materialmay be TCP, hydroxyapatite, mineral recovered from bone, cancellouschips, cortical chips, surface demineralized bone, or other material.The osteoinductive material may be combined with a further carrier suchas starch or glycerol. Accordingly, in some embodiments, the partiallydemineralized bone may act as a carrier for the tissue-derived extract.

The osteoinductive composition, comprising partially demineralized boneand, in some embodiments, tissue-derived extract and carrier, may becompletely insoluble or may be slowly solubilized after implantation.Following implantation, the composition may resorb or degrade, remainingsubstantially intact for at least one to seven days, or for two or fourweeks or longer and often longer than 60 days. The composition may thusbe resorbed prior to one week, two weeks, three weeks, or other,permitting the entry of bone healing cells.

In various embodiments, the partially demineralized bone may be bondedtogether to provide a solid, coherent aggregate through engagement withparticles of binding agent present on the surfaces of the partiallydemineralized bone. Reference is made to U.S. Pat. Nos. 6,696,073,6,478,825, 6,440,444, and 6,294,187, and to U.S. Patent PublicationsNos. 2006/0216323 and 2005/0251267, all herein incorporated byreference.

Provide Partially Demineralized Bone in Covering

As shown in block 22 of FIG. 1, in some embodiments the composition,including the surface-demineralized bone particles, presseddemineralized bone fibers, tissue derived extract, and/or carrier, maybe provided in a containment covering, such as a porous mesh, to providea delivery system. Generally, the covering may be biocompatible andresorb able.

In some embodiments, surface demineralized bone particles, andoptionally demineralized bone fibers, may be provided in a covering suchthat the covering provides a focus or concentration of biologicalactivity and maintains the surface demineralized bone particles anddemineralized bone fibers in spatial proximity to one another, possiblyto provide a synergistic effect. The covering further may controlavailability of the surface demineralized bone particles anddemineralized bone fibers to cells and tissues of a surgical site overtime. In some embodiments, the delivery system may be used for deliverythrough a limited opening, such as in minimally invasive surgery ormini-open access. In some embodiments, the delivery system may be usedto deliver morselized or particulated materials (the substance providedin the covering) in pre-measured amounts.

The covering may have a single compartment or may have a plurality ofcompartments. Thus, in one embodiment, the covering comprises first andsecond compartments. The surface demineralized bone particles may beprovided in the first compartment and the demineralized bone fibers maybe provided in the second compartment. The second compartment may beadjacent, apart from, inside, or surrounding the first compartment. Inalternative embodiments, a blend of surface demineralized particles,demineralized bone fibers, tissue-derived extract, and/or othermaterials may be provided in either or both of first compartment and thesecond compartment.

In use, the partially demineralized bone particles, and demineralizedbone matrix if provided, may be placed in the covering prior toimplantation of the covering in the body. In alternative embodiments,the covering may be implanted in the body and the partiallydemineralized bone particles, and demineralized bone matrix if provided,may be placed in the covering thereafter.

In various embodiments, the covering may comprise a polymer (such aspolyalkylenes (e.g., polyethylenes, polypropylenes, etc.), polyamides,polyesters, polyurethanes, poly(lactic acid-glycolic acid), poly(lacticacid), poly(glycolic acid), poly(glaxanone), poly(orthoesters),poly(pyloric acid), poly(phosphazenes), L-co-G, etc.), otherbioabsorbable polymer such as Dacron or other known surgical plastics, anatural biologically derived material such as collagen, a ceramic (withbone-growth enhancers, hydroxyapatite, etc.), PEEK(polyether-etherketone), desiccated biodegradable material, metal,composite materials, a biocompatible textile (e.g., cotton, silk,linen), or other. In one embodiment, the containment covering is formedas a long tube-like covering and may be used with minimally invasivetechniques.

IX. Form an Implant

The osteoimplant resulting from the partially demineralized bone,demineralized bone matrix, tissue-derived extract, and/or carrier may beflowable, have a putty or gel-like consistency, may be shaped or molded,may be provided as a slurry, may be deformable, and/or may comprisesubstantially dry pieces held together in a covering. The osteoimplantmay comprise a monolithic bone or may comprise an aggregate of smallerbone elements. The osteoimplant may assume a determined or regular formor configuration such as a sheet, plate, disk, tunnel, cone, or tube, toname but a few. Prefabricated geometry may include, but is not limitedto, a crescent apron for single site use, an I-shape to be placedbetween teeth for intra-bony defects, a rectangular bib for defectsinvolving both the buccal and lingual alveolar ridges, neutralizationplates, reconstructive plates, buttress plates, T-buttress plates, spoonplates, clover leaf plates, condylar plates, compression plates, bridgeplates, or wave plates. Partial tubular as well as flat plates can befabricated from the osteoimplant. Such plates may include suchconformations as, e.g., concave contoured, bowl shaped, or defectshaped. The osteoimplant can be machined or shaped by any suitablemechanical shaping means. Computerized modeling can provide for theintricately-shaped three-dimensional architecture of an osteoimplantcustom-fitted to the bone repair site with great precision. Inembodiments wherein the osteoimplant is shaped or moldable, the implantmay retain coherence in fluids.

Accordingly, the osteoinductive composition, especially when comprisingas an aggregate of particles, may be subjected to a configuring step toform an osteoimplant. The configuring step can be employed usingconventional equipment known to those skilled in the art to produce awide variety of geometries, e.g., concave or convex surfaces, steppedsurfaces, cylindrical dowels, wedges, blocks, screws, and the like. Asurgically implantable material fabricated from elongated bone particlesthat have been demineralized, which may be shaped as a sheet, andprocesses for fabricating shaped materials from demineralized boneparticles is disclosed in U.S. Pat. Nos. 5,507,813 and 6,436,138,respectively, the contents of which are herein incorporated byreference. Suitable sheets include those sold under the trade nameGrafton® DBM Flex, which must be wetted/hydrated prior to use to beuseful for implantation. Such sheets have recently been reported aseffective in seeding human bone marrow stromal cells (BMSCs), which maybe useful in the repair of large bone defects. Kasten et al.,“Comparison of Human Bone Marrow Stromal Cells Seeded onCalcium-Deficient Hydroxyapatite, Betatricalcium Phosphate andDemineralized Bone Matrix,” Biomaterials, 24(15):2593-603, 2003. Alsouseful are demineralized bone and other matrix preparations comprisingadditives or carriers such as binders, fillers, plasticizers, wettingagents, surface active agents, biostatic agents, biocidal agents, andthe like. Some exemplary additives and carriers include polyhydroxycompounds, polysaccharides, glycosaminoglycan proteins, nucleic acids,polymers, poloxamers, resins, clays, calcium salts, and/or derivativesthereof.

In some embodiments, the osteoinductive composition may have improvedspatial properties, such as material handling and packing properties.Unlike DBM, surface demineralized or mineralized particles do notgenerally entangle and hold together. Tissue-derived extracts havinglarge amounts of collagen type I or collagen type I residues, forexample a collagenous extract, can impart handling and packingproperties to surface demineralized bone particles. Thus, anosteoinductive composition comprising surface demineralized boneparticles and such tissue-derived extract generally may have betterremodeling properties than surface demineralized bone alone. Theimproved remodeling properties can further be enhanced by a carrier. Insome embodiments, the partially demineralized bone particles may beforced into close proximity, resulting in better osteoconduction. Somecarriers may be especially suited for providing improved materialhandling and packing properties. These include, for example hydrogelssuch as chitosan and fast resorbing formulations of L-co-G. In someembodiments, the osteoinductive composition may comprise partially orfully demineralized bone particles having an improved packingefficiency.

X. Formulation

The osteoinductive composition, the delivery vehicle (including carrieror covering), or the osteoimplant may be formulated for a particularuse. The formulation may be used to alter the physical, biological, orchemical properties of the composition or the carrier. A physician wouldreadily be able to determine the formulation needed for a particularapplication, taking into account such factors as the type of injury, thesite of injury, the patient's health, and the risk of infection. Invarious embodiments, the osteoinductive composition may comprise, forexample less than approximately 0.5% water, less than approximately 1%water, or less than approximately 5% water.

Osteoinductive compositions or osteoimplants therefore may be preparedto have selected resorption/loss of osteoinductivity rates, or even tohave different rates in different portions of an implant. For example,the formulation process may include the selection of partiallydemineralized particles of a particular size or composition, combinedwith the selection of a particular stabilizing agent or agents, and theamounts of such agents.

In one example, an osteoimplant may be provided whose tissue-derivedextract comprises osteoinductive factors that are active in a relativelyconstant amount over a given period of time. An osteoimplant comprisingfactors with longer half-lives can be prepared using a lessbiodegradable polymer or a larger amount (e.g., a thicker coating) ofpolymeric compound. Alternatively or additionally, the particle size ofthe partially demineralized bone may be important in determining thehalf-life of the osteoimplant. In certain embodiments, an osteoinductivecomposition may include a mixture of particles, each with a differenthalf-life. Such a mixture could provide the steady or possible unmaskingof osteoinductive factors over an extended period of time ranging fromdays to weeks to months depending on the needs of the injury.Compositions such as this can be formulated to stimulate bone growth ina human patient comparable to the bone growth induced by treatment with10 μg of rhBMP on a collagen sponge, and preferably comparable to 100μg, and most preferably 1-10 mg rhBMP. When the degradation of theosteoimplant is of concern, it may be desirable to test the shelf-lifeof the osteoimplant to determine shelf-life at, for example, 1, 2, or 3years. This may be done by storing the osteoimplant at, for example,room temperature or, for accelerated testing, 38° C., and periodicallychecking the inductivity of the osteoimplant. Reference is made toPCT/US05/003092, which is hereby incorporated by reference herein.Implants with enhanced shelf lives may retain more than about 75% andabout 80% of their osteoinductivity after as long as, or longer than,three years.

Physical properties such as deformability and viscosity of the carriermay also be chosen depending on the particular clinical application. Thepartially demineralized bone may be mixed with other materials andfactors to improve other characteristics of the implant. For example,the partially demineralized bone may be mixed with other agents toimprove wound healing. These agents may include drugs, proteins,peptides, polynucleotides, solvents, chemical compounds, and biologicalmolecules.

Further, the composition may be formulated to be settable and/orinjectable. Thus, for example, the composition may be injectable througha 10-gauge, a 12-gauge, or an 18-gauge needle.

Accordingly, in some embodiments the composition may be substantiallysolid pieces, rubbery, rubbery with chunks, stiff (as freeze-dried),stiff with chunks, putty, paste, flowable, or injectable. The term“flowable” in this context applies to compositions whose consistenciesrange from those which can be described as shape-sustaining but readilydeformable, e.g., those which behave like putty, to those which arerunny. Specific forms of flowable bone powder compositions includecakes, pastes, creams and fillers. Reference is made to U.S. Pat. No.5,290,558, herein incorporated by reference in its entirety, fordiscussion of flowable materials.

Also as previously discussed, the osteoinductive composition may beformed into various shapes and configurations, including rods, strings,sheets, weaves, solids, cones, discs, fibers, and wedges. Such shapesmay result from a monolithic bone piece or an aggregate of boneparticles. In certain embodiments, the shape and size of the partiallydemineralized bone affect the time course of osteoinductivity. Forexample, in a cone or wedge shape, the tapered end will result inosteoinductivity shortly after implantation of the osteoimplant, whereasthe thicker end will lead to osteoinductivity later in the healingprocess (hours to days to weeks later). In certain embodiments ofosteoimplants comprising an aggregate of bone particles, the particleshave a length of greater than 2 mm, greater than 1.5 mm, greater than 1mm, greater than 500 microns, or greater than 200 microns across itswidest dimension. Also, larger particle size will induce bone formationover a longer time course than smaller particles. Particles of differentcharacteristics (e.g., composition, size, shape) may be used in theformation of these different shapes and configurations. For example, ina sheet of partially demineralized bone, a layer of long half-lifeparticles may be alternated between layers of shorter half-lifeparticles. See U.S. Pat. No. 5,899,939, herein incorporated byreference, for suitable examples. In a weave, strands composed of shorthalf-life particles may be woven together with strands of longerhalf-lives.

In one embodiment, fibrous partially demineralized bone may be shapedinto a matrix form as described in U.S. Pat. No. 5,507,813, hereinincorporated by reference. The shaped partially demineralized bone maythen be embedded within a diffusion barrier type matrix, such that aportion of the matrix is left exposed free of the matrix material.Suitable blocking matrices are starch, phosphatidyl choline, tyrosinepolycarbonates, tyrosine polyarylates, polylactides, polygalactides, orother resorbable polymers or copolymers. Devices prepared in this wayfrom these matrices have a combination of immediate and longer lastingosteoinductive properties and are particularly useful in promoting bonemass formation in human posterolateral spine fusion indications.

In another embodiment, carriers having a pre-selected three-dimensionalshape may be prepared by repeated application of individual layers ofpartially demineralized bone, for example by 3-D printing as describedby U.S. Pat. Nos. 5,490,962, 5,518,680, and 5,807,437, each incorporatedherein by reference. Different layers may comprise individual stabilizedpartially demineralized bone preparations, or alternatively may comprisepartially demineralized bone layers treated with stabilizing agentsafter deposition of multiple layers.

In the process of preparing the osteoimplant, the materials may beproduced entirely aseptically or be sterilized to eliminate anyinfectious agents such as HIV, hepatitis B, or hepatitis C. Thesterilization may be accomplished using antibiotics, irradiation,chemical sterilization (e.g., ethylene oxide), or thermal sterilization.Other methods known in the art of preparing DBM such as defatting,sonication, and lyophilization may also be used in preparing a DBMcarrier. Since the biological activity of demineralized bone is known tobe detrimentally affected by most terminal sterilization processes, caremust be taken when sterilizing the inventive compositions.

XI. Optional Additives

Optionally, other additives may be included in the osteoconductivecomposition. It will be appreciated that the amount of additive usedwill vary depending upon the type of additive, the specific activity ofthe particular additive preparation employed, and the intended use ofthe composition. The desired amount is readily determinable by the user.

Any of a variety of medically and/or surgically useful optionalsubstances can be incorporated in, or associated with, theosteoinductive factors either before, during, or after preparation ofthe osteoinductive composition. Thus, for example when demineralizedbone particles are used to form the material, one or more of suchsubstances may be introduced into the demineralized bone particles, forexample, by soaking or immersing the bone particles in a solution ordispersion of the desired substance(s).

Medically/surgically useful substances that can be readily combined withthe partially demineralized bone include, for example, collagen,insoluble collagen derivatives, etc., and soluble solids and/or liquidsdissolved therein, e.g., antiviricides, particularly those effectiveagainst HIV and hepatitis; antimicrobials and/or antibiotics such aserythromycin, bacitracin, neomycin, penicillin, polymyxin B,tetracyclines, viomycin, chloromycetin and streptomycins, cefazolin,ampicillin, azactam, tobramycin, clindamycin and gentamicin, etc.;biocidal/biostatic sugars such as dextroal, glucose, etc.; amino acids,peptides, vitamins, inorganic elements, co-factors for proteinsynthesis; hormones; endocrine tissue or tissue fragments; synthesizers;enzymes such as collagenase, peptidases, oxidases, etc.; polymer cellscaffolds with parenchymal cells; angiogenic drugs and polymericcarriers containing such drugs; collagen lattices; antigenic agents;cytoskeletal agents; cartilage fragments, living cells such aschondrocytes, bone marrow cells, mesenchymal stem cells, naturalextracts, tissue transplants, bone, demineralized bone powder,autogenous tissues such blood, serum, soft tissue, bone marrow, etc.;bioadhesives, bone morphogenic proteins (BMPs), angiogenic factors,transforming growth factor (TGF-beta), insulin-like growth factor(IGF-1); growth hormones such as somatotropin; bone digestors; antitumoragents; immuno-suppressants; permeation enhancers, e.g., fatty acidesters such as laureate, myristate and stearate monoesters ofpolyethylene glycol, enamine derivatives, alpha-keto aldehydes, etc.;and, nucleic acids. The amounts of such optionally added substances canvary widely with optimum levels being readily determined in a specificcase by routine experimentation.

Bone regeneration involves a multitude of cells (e.g. cartilage,fibroblasts, endothelial, etc.) besides osteoblasts. Stem cells may becombined with the partially demineralized bone. Accordingly, theosteoinductive composition may be used to deliver stem cells, whichoffers the potential to give rise to different types of cells in thebone repair process

In certain embodiments, the additive is adsorbed to or otherwiseassociated with the osteoinductive composition. The additive may beassociated with the osteoinductive composition through specific ornon-specific interactions, or covalent or noncovalent interactions.Examples of specific interactions include those between a ligand and areceptor, an epitope and an antibody, etc. Examples of nonspecificinteractions include hydrophobic interactions, electrostaticinteractions, magnetic interactions, dipole interactions, van der Waalsinteractions, hydrogen bonding, etc. In certain embodiments, theadditive is attached to the osteoinductive composition, for example, tothe carrier, using a linker so that the additive is free to associatewith its receptor or site of action in vivo. In other embodiments theadditive is either covalently or non-covalently attached to the carrier.In certain embodiments, the additive may be attached to a chemicalcompound such as a peptide that is recognized by the carrier. In anotherembodiment, the additive is attached to an antibody, or fragmentthereof, that recognizes an epitope found within the carrier. In certainembodiments at least additives are attached to the osteoimplant. Inother embodiments at least three additives are attached to theosteoinductive composition. An additive may be provided within theosteoinductive composition in a sustained release format. For example,the additive may be encapsulated within biodegradable nanospheres,microspheres, etc.

It will be understood by those skilled in the art that the lists ofoptional substances herewith included are not intended to be exhaustiveand that other materials may be admixed with bone-derived elementswithin the practice of the present invention.

In one embodiment, the osteoconductive composition further comprises acell such as an osteogenic cell or a stem cell. In various embodiments,the additive may comprise radiopaque substances, angiogenesis promotingmaterials, bioactive agents, osteoinducing agents, or other. Referenceis made to U.S. patent application Ser. Nos. 11/555,606 and 11/555,608for specific discussion of possible additives.

XII. Assessment of Osteogenic Activity

Any suitable manner for assessing osteogenic activity may be used.Generally, the more closely the manner of assessing osteoinductivitycorrelates with the anticipated use of the osteoinductive composition,the more predictive the results will be of how the osteoinductivecomposition will perform in a human. Thus, for example, a sheepvertebral model may be used to assess osteogenic activity of theosteoinductive composition.

In various embodiments, the osteoinductive composition may have aninductivity exceeding that of between 2 and 20 volumes of mineralizedbone that is prepared into demineralized bone. For example, theosteoinductive composition may have an inductivity exceeding that ofapproximately five volumes of mineralized bone that is prepared intodemineralized bone. In some embodiments, one gram of the osteoinductivecomposition may have inductivity exceeding that of demineralized boneprepared from five grams of mineralized allograft bone.

Induction of bone formation can be determined by a histologicalevaluation showing the de novo formation of bone with accompanyingosteoblasts, osteoclasts, and osteoid matrix. For example,osteoinductive activity of an osteoinductive factor can be demonstratedby a test using a substrate onto which material to be tested isdeposited. The substrate with deposited material is implantedsubcutaneously in a test animal. The implant is subsequently removed andexamined microscopically for the presence of bone formation includingthe presence of osteoblasts, osteoclasts, and osteoid matrix. A suitableprocedure for assessing osteoinductive activity is illustrated inExample 5 of U.S. Pat. No. 5,290,763, herein incorporated by reference.Although there is no generally accepted scale of evaluating the degreeof osteogenic activity, certain factors are widely recognized asindicating bone formation. Such factors are referenced in the scale of0-8 which is provided in Table 3 of example 1 of U.S. Pat. No.5,563,124, herein incorporated by reference. The 0-4 portion of thisscale corresponds to the scoring system described in U.S. Pat. No.5,290,763, which is limited to scores of 0-4. The remaining portion ofthe scale, scores 5-8, references additional levels of maturation ofbone formation. The expanded scale also includes consideration ofresorption of collagen, a factor which is not described in the '763patent. Osteoinductivity may be assessed in tissue culture, e.g. as theability to induce an osteogenic phenotype in culture cells (primary,secondary, cell lines, or explants). Cell culture assays measure theability of a matrix to cause one or more features indicative ofdifferentiation along an osteoblastic or chondrocytic lineage. Thefeature(s) can be an expression of a marker characteristic ofdifferentiation along an osteoblastic or chondrocytic lineage, e.g. amarker that is normally expressed by osteoblast precursors, osteoblasts,chondrocytes, or precursors of chondrocytes. One suitable marker isalkaline phosphatase. Reference is made to U.S. patent application Ser.No. 11/683,938, herein incorporated by reference, for discussion ofalternative in vitro assay methods.

In studies, a typical amount of DBM for implantation is 20 mg in a mouseand 40 mg in a rat. Significant increases in the growth factor dose, forexample, 150× dose (or 150 times the growth factor found in normal DBM),lead to significantly more and potentially faster bone growth withlarger volume bone growth, more dense bone growth, larger nodules ofbone growth, higher x-ray density, and, generally, a higherosteoinductive score. Associated with this increase in osteoinductivitycan be a cortical shell surrounding the nodule and some level ofvascularization in the nodule. However, the ability to quantitativelymeasure is generally limited by the method used, and generally measuredincreases in osteoinductive activity are not linear with the increase indosage. Thus, if 20 mg of DBM gives an osteoinductive activity of 1, 100times the growth factor dose (2000 mg of DBM growth factors) does notgive an osteoinductive activity of 100. Instead, it may result in anosteoinductive activity of about 20. A limitation of measurement usingosteoinductive scores is that, in some situations, the system's abilityto respond may be saturated. Thus, for example, if the score ranges onlyfrom 1 to 4, two samples may have the same score (4) but may not, infact, be comparable. This is particularly the case when the boneresulting from one method or implant is qualitatively better than thebone resulting from another method or implant. That is, both methods orimplants may result in an osteoinductive score of 4 but one may resultin qualitatively better bone than the other. Thus, in some situations itmay be desirable to test speed of growth, density, presence of corticalbone, shelling, and/or other factors showing an increase over normaldemineralized bone matrix. Further, in addition to, or in lieu of,testing at 28 days, it may be desirable to test inductivity at 21 daysGenerally, inductivity may be measured histomorphometrically by methodsknown in art.

Further, delivering 100 times the growth factor dose may be challenging.In filling a bone defect, only as much filler may be used as there isbone void space.

XIII. Examples

The examples may refer to particles, particles formed into a putty,particles formed into a gel, or other. It is to be understood that theexamples are illustrative only and are not intended to be limiting.Thus, each example may be modified to provide compositions havingdiffering consistencies such as flowable, injectable, rubbery, flexible,stiff, or other.

Example 1 Surface Demineralized Heat Treated Particles

In one example, bone was cleaned of soft tissue and ground to powderranging from 2.8 mm to 4 mm. The particles were extracted with 1:1chloroform-methanol for 6 hours. The solvent was then decanted and theexcess allowed to evaporate under a fume hood overnight. The particleswere then vacuum dried overnight.

The particles were surface demineralized for 75 minutes in 0.6 N HCl andthen washed with distilled water until the pH of the wash exceeded 3.0.The resulting surface demineralized particles were then incubated withagitation in 100 mM phosphate buffer, pH 7.4, containing 6.0 mM NEM and2.0 mM sodium azide for 72 hours at 37° C.

The resulting particles were washed two times for 15 minutes in water atroom temperature. The particles were lyophilized and implanted in asheep femoral defect; the results were examined by micro-CT analysis 4weeks and 13 weeks post-implantation.

FIG. 5 illustrates the 13 week results of autograft and of surfacedemineralized heat treated particles.

Example 2 Surface Demineralized Heat Treated Particles

The particles are prepared as described in Example 1 exceptingincubation in phosphate buffer.

Example 3a Smaller Surface Demineralized Heat Treated Particles

Particles were ground to a size ranging from 1 mm to 2.8 mm anddemineralized in 0.6N HCl for 60 minutes prior to heat treatment asdescribed in Example 1.

Example 3b Smaller Surface Demineralized Heat Treated Particles

Particles were ground to a size ranging from 0.5 mm to 1.0 mm anddemineralized in 0.6N HCl for 10 minutes prior to heat treatment asdescribed in Example 1.

Example 3c Smaller Surface Demineralized Heat Treated Particles

Particles were ground to a size ranging from 0.1 mm to 0.5 mm anddemineralized in 0.6N HCl for 7 minutes prior to heat treatment asdescribed in Example 1.

Example 4a Various Degrees of Demineralization

Particles are ground to a size ranging from 1.0 mm to 2.8 mm anddemineralized for 15 minutes prior to heat treatment as described inExample 1.

Example 4b Various Degrees of Demineralization

Particles are ground to a size ranging from 1.0 mm to 2.8 mm anddemineralized for 30 minutes prior to heat treatment as described inExample 1.

Example 4c Various Degrees of Demineralization

Particles are ground to a size ranging from 1.0 mm to 2.8 mm anddemineralized for 120 minutes prior to heat treatment as described inExample 1.

Example 4d Various Degrees of Demineralization

Particles are ground to a size ranging from 1.0 mm to 2.8 mm anddemineralized for 240 minutes prior to heat treatment as described inExample 1.

Example 4e Various Degrees of Demineralization

Particles are ground to a size ranging from 1.0 mm to 2.8 mm anddemineralized for 480 minutes prior to heat treatment as described inExample 1.

Example 4f Various Degrees of Demineralization

Particles are ground to a size ranging from 1.0 mm to 2.8 mm and fullydemineralized prior to heat treatment as described in Example 1.

Example 4g Various Degrees of Demineralization

Particles are ground to a size ranging from 2.8 mm to 4.0 mm anddemineralized for 15 minutes prior to heat treatment as described inExample 1.

Example 4h Various Degrees of Demineralization

Particles are ground to a size ranging from 2.8 mm to 4.0 mm anddemineralized for 240 minutes prior to heat treatment as described inExample 1.

Example 4i Various Degrees of Demineralization

Particles are ground to a size ranging from 2.8 mm to 4.0 mm anddemineralized for 480 minutes prior to heat treatment as described inExample 1.

Example 4j Various Degrees of Demineralization

Particles are ground to a size ranging from 2.8 mm to 4.0 mm and fullydemineralized prior to heat treatment as described in Example 1.

Example 4k Various Degrees of Demineralization

Particles are treated as described in Example 1 and above exceptingincubation in phosphate buffer.

Example 5a Mixing of Surface Demineralized Particles with DBM Fiber

Particles are made as in Example 1 and mixed with demineralized bonefibers in a ratio of 3 volumes of surface demineralized particles to 1volume of DBM fiber.

Example 5b Mixing of Surface Demineralized Particles with DBM Fiber

Particles are made as in Example 1 and mixed with demineralized bonefibers in a ratio of 1 volume of surface demineralized particles to 1volume of DBM fiber.

Example 5c Mixing of Surface Demineralized Particles with DBM Fiber

Particles are made as in Example 1 and mixed with demineralized bonefibers in a ratio of 2 volume of surface demineralized particles to 1volume of DBM fiber.

Example 6a Combining Surface Demineralized Heat Treated Particles withDBM Extracts

Particles made as in Example 1 are mixed with protein extracted from anequal volume of demineralized bone matrix with 4 M Guanidine HCl. Theextracted proteins are added to the surface demineralized particles andthe suspension is dialyzed against water until the guanidine iseffectively removed. The preparation is then lyophilized.

Example 6b Combining Surface Demineralized Heat Treated Particles withDBM Extracts

Particles made as in Example 1 are mixed with protein extracted fromtwice the volume of demineralized bone matrix with 4 M Guanidine HCl.The extracted proteins are added to the surface demineralized particlesand the suspension is dialyzed against water until the guanidine iseffectively removed. The preparation is then lyophilized.

Example 6c Combining Surface Demineralized Heat Treated Particles withDBM Extracts

Particles made as in Example 1 are mixed with protein extracted fromfive times the volume of demineralized bone matrix with 4 M GuanidineHCl. The extracted proteins are added to the surface demineralizedparticles and the suspension is dialyzed against water until theguanidine is effectively removed. The preparation is then lyophilized.

Example 6d Combining Surface Demineralized Heat Treated Particles withDBM Extracts

Particles made as in Example 1 are mixed with protein extracted from tentimes the volume of demineralized bone matrix with 4 M Guanidine HCl.The extracted proteins are added to the surface demineralized particlesand the suspension is dialyzed against water until the guanidine iseffectively removed. The preparation is then lyophilized.

Example 7 Organic Precipitation of Proteins

Materials are prepared as in Example 6 excepting precipitation ofproteins onto surface demineralized bone with a volume of 1:1acetone/ethanol equal to the volume of guanidine HCl.

Example 8 Combining Surface Demineralized Heat Treated Particles withDemineralized Bone Fibers and Protein Extracts

Mixtures of surface demineralized particles and demineralized bonematrix fibers described in Example 5 are combined with extracts asdescribed in Examples 6 and 7.

Example 9a Combining Surface Demineralized Heat Treated Particles with aCarrier

Compositions as prepared by any of Examples 1-8 are combined withglycerol.

Example 9b Combining Surface Demineralized Heat Treated Particles with aCarrier

Compositions as prepared by any of Examples 1-8 are combined with apolylactide polymer.

Example 9c Combining Surface Demineralized Heat Treated Particles with aCarrier

Compositions as prepared by any of Examples 1-8 are combined with apolyglycolide polymer.

Example 9d Combining Surface Demineralized Heat Treated Particles with aCarrier

Compositions as prepared by any of Examples 1-8 are combined with apolylactide-co-glycolide copolymer.

Example 9e Combining Surface Demineralized Heat Treated Particles with aCarrier

Compositions as prepared by any of Examples 1-8 are combined with astarch.

Example 9f Combining Surface Demineralized Heat Treated Particles with aCarrier

Compositions as prepared by any of Examples 1-8 are combined with analginate.

Example 9g Combining Surface Demineralized Heat Treated Particles with aCarrier

Compositions as prepared by any of Examples 1-8 are combined withchitosan.

Example 9h Combining Surface Demineralized Heat Treated Particles with aCarrier

Compositions as prepared by any of Examples 1-8 are combined with apluronic.

Example 9i Combining Surface Demineralized Heat Treated Particles with aCarrier

Compositions as prepared by any of Examples 1-8 are combined withhyaluronic acid.

Example 10

Sheep cortical bone is processed to different components: 1-2.8 mmsurface demineralized particles, DBM fibers and DBM powder (106-500 μm).DBM powder is extracted with 4M guanidine HCl. The guanidinehydrochloride extract is dialyzed against water and the supernatant andprecipitate are separated via centrifugation. The collagenoussupernatant is lyophilized to obtain dry collagen residue. 10 grams ofdry surface demineralized bone are combined with 3.85 grams of dry DBMfiber and 0.85 grams dry collagen residue. The material is mixed in thepresence of 20 ml water. The final mixture is injected into a mold,lyophilized to form a matrix.

Example 11

Composition is formed as in Example 10 but omitting the centrifugationof the extract and separation of supernatant from precipitate.

Example 12

Composition is formed as in Example 10 excepting that mixing in thefinal step is carried out in a solution of glycerol and water in avolume ratio of 45:55.

Example 13

Sheep cortical bone is processed to different components: 1-2.8 mmsurface demineralized particles and DBM fibers. 10 grams of dry surfacedemineralized bone are combined with 3.85 grams of dry DBM fiber and0.15 grams of chitosan. Prior to mixing the chitosan is dissolved in 5ml of 2% acetic acid. The materials are mixed in the presence of 15 mlwater. The final mixture is injected into a mold, lyophilized to form amatrix. The matrix is then treated with 5% sodium citrate for 1 hour,washed and lyophilized.

Example 14

Composition is prepared as in example 13 excepting the use of 15 ml45:55 glycerol-water in place of 15 ml water and excluding treatmentwith sodium citrate.

Example 15

Sheep cortical bone is processed to different components: 1-2.8 mmsurface demineralized particles and DBM powder (106-500 μm). DBM powderis extracted with 4M guanidine HCl. The guanidine hydrochloride extractis dialyzed against water and the supernatant and precipitate areseparated via centrifugation. The collagenous supernatant is lyophilizedto obtain dry collagen residue. 10 g surface demineralized particles arewetted in 40 ml DI water and then pressed at 4000 psi. Pressed surfacedemineralized particles are soaked in a mixture of glycerol/water(45/55) for 1 hour and then filtered to get around 23 grams ofglycerated material. The glycerated surface demineralized particles arefurther combined with 1.1 grams of collagen residue in 5 ml water. Thefinal mixture is injected into a mold and lyophilized to obtain amatrix.

Example 16

Composition prepared as in Example 14 but omitting the centrifugationstep and separation of supernatant from precipitate.

Example 17

Sheep cortical bone is processed to different components: 1-2.8 mmsurface demineralized particles and DBM fibers. 10 grams of dry surfacedemineralized bone are combined with 3.85 grams of dry DBM fiber and0.10 grams of human or bovine derived antelocollagen. Prior to mixingthe collagen is suspended in 10 ml of 2% lactic acid. The materials aremixed in the presence of 10 ml water. The final mixture is injected intoa mold, lyophilized to form a matrix.

Example 18

Sheep cortical bone is processed to different components: 1-2.8 mmsurface demineralized particles and DBM fibers. 10 grams of dry surfacedemineralized bone are combined with 3.85 grams of dry DBM fiber and0.50 grams of polymer. Polymers can be naturally derived or syntheticsuch as alginate, cellulose, gelatin, poly(lactic acid),poly(lactic-co-glycolic acid), poly(caprolactone),poly(lactide-co-caprolactone), poly(carbonate), Pluronic F127 etc. Priorto mixing the polymers are dissolved in a biocompatible solvent. Thecomponents are mixed and injected into a mold, lyophilized to form amatrix.

Example 19

Sheep cortical bone is processed to different components: 1-2.8 mmsurface demineralized particles, DBM fibers and DBM powder (106-500 μm).DBM powder is extracted with 4M guanidine HCl. The guanidinehydrochloride extract is dialyzed against water and the supernatant andprecipitate are separated via centrifugation. The collagenoussupernatant is lyophilized to obtain dry collagen residue. 10 grams ofdry surface demineralized bone are combined with 3.85 grams of dry DBMfiber and 0.85 grams dry collagen residue. The material is mixed in thepresence of 20 ml of water and loaded into a syringe. Any excess wateris extruded.

Example 20

Composition is prepared as in example 19 but omitting the centrifugationof the extract and separation of supernatant from precipitate.

Example 21

Composition is prepared as in Example 19 excepting that mixing in thefinal step is carried out in a solution of glycerol and water in avolume ratio of 45:55.

Example 22

Sheep cortical bone is processed to different components: 1-2.8 mmsurface demineralized particles and DBM fibers. 10 grams of dry surfacedemineralized bone are combined with 3.85 grams of dry DBM fiber and0.15 grams of chitosan. Prior to mixing the chitosan is dissolved in 5ml of 2% acetic acid. The materials are mixed in the presence of 15 mlwater. The material is loaded into a syringe to obtain an extrudableformulation.

Example 23

Composition is prepared as in Example 22 excepting the use of 15 ml45:55 glycerol-water in place of 15 ml water.

Example 24

Sheep cortical bone is processed to different components: 1-2.8 mmsurface demineralized particles, DBM fibers. 10 grams of dry surfacedemineralized bone are combined with 3.85 grams of dry DBM fiber and 8.3grams of hydrated starch. The material is loaded into a syringe toobtain an extrudable formulation.

Example 25

Sheep cortical bone is processed to different components: 1-2.8 mmsurface demineralized particles and DBM fibers. 10 grams of dry surfacedemineralized bone are combined with 3.85 grams of dry DBM fiber and0.10 grams of human or bovine derived predominantly type I collagen.Prior to mixing the collagen is suspended in 10 ml of 2% lactic acid.The materials are mixed in the presence of 10 ml water. The material isloaded into a syringe to obtain an extrudable formulation.

XIV. Assessment of Bone Particles

It may be useful to assess characteristics of the bone particles attimes before, during, or after the methods provided herein.

Assessment of Neutral Protease Activity

It may be useful to assess endogenous protease activity in the boneparticles. For example, in the method shown in FIG. 2, the neutralprotease activity of mineralized bone is high but is reduced upondemineralization. Accordingly, the surface of the particles afterdemineralization has a lower protease activity than prior todemineralization. The lower protease activity allows maintenance ofosteoinductive activity at the particle surface. Any suitable method ofassessing protease activity may be used.

In one embodiment, the following procedure was used to assess endogenousprotease activity of the bone particles. A Pierce QuantiCleave ProteaseActivity Kit was used. In the embodiment herein described, a modifiedcasein substrate was used. The kit identifies exposed N-terminal aminesof peptides released from the casein precursor.

All samples were processed using sterile technique. Microfuge tubes andpipette tips were autoclaved.

Generation of Finely Powdered Sterile DBM and Nondemineralized Bone

A. 1 gram of human DBM was prepared and finely powdered in a SpecFreezer Mill using the following protocol:

5 min pre-cool in LN2. (T3)

3×2 min cycles (T1)

1 min interim cooling. (T2)

B. 1 gram of powdered nondemineralized bone (mixed batches), cleaned andsonicated in ethanol, was treated as above.

Preparation of Assay Solution

PBS was used as the Assay Buffer instead of 50 mM Borate Buffer. Thiscomprised adding 5 ml of PBS to 3 vials (10 mg) of Succinylated casein,letting stand for 5 min and gently swirling to dissolve the protein. Thecontents of three vials were sterile filtered into a single 15 mlSterileTube. This is known as the sterile succinylated casein solution.The volume of the sterile succinylated casein solution was adjusted to15 ml using sterile PBS.

300 μl of succinylated casein solution was added to each of five tubesfrom each group.

As blanks, 300 μl of phosphate buffered saline, pH 7.4, containing 0.9mM CaCl₂, 0.2H₂O and 0.5 mM MgCl₂ was added to five tubes from eachgroup. All tubes were vortexed for 20 seconds and then placed on ice for15 minutes. The tubes were centrifuged at 12,000 rpm for 5 minutes andthe vortexing and centrifugation steps were repeated.

Protease Assay

TPCK trypsin stock solution was prepared by adding 5 mg TPCK trypsin(included with Kit) to 2.5 ml of PBS. The solution was sterile filteredinto a sterile 15 ml tube and the volume was raised to 10 ml.

The stock solution was serially diluted in a sterile hood by adding 1 mlof stock to 9 mo of PBS, vortexing, and continuing the 10 fold dilutionseries for a total of 9 standards ranging from 5.0×10⁻¹ mg/ml to5.0×10⁻⁹ mg/ml.

All samples received an additional 200 ul Casein/or 200 ul PBS.

The Standards

100 ml of succinylated casein solution was added to each of 21 sterilemicrofuge tubes.

The following tubes were prepared and processed as described:

1. 0.0 ng/ml trypsin To three of the tubes add 50 ul of sterile PBS. 2.0.005 ng/ml trypsin To three of the tubes add 50 ul 5.0 × 10⁻⁹ mg/mltrypsin 3. 0.05 ng/ml trypsin To three of the tubes add 50 ul 5.0 × 10⁻⁸mg/ml trypsin. 4. 0.5 ng/ml trypsin To three of the tubes add 50 ul 5.0× 10⁻⁷ mg/ml trypsin. 5. 5.0 ng/ml trypsin To three of the tubes add 50ul 5.0 × 10⁻⁶ mg/ml trypsin. 6. 50.0 ng/ml trypsin To three of the tubesadd 50 ul 5.0 × 10⁻⁵ mg/ml trypsin 7. 500.0 ng/ml trypsin To three ofthe tubes add 50 ul 5.0 × 10⁻⁴ mg/ml trypsin 8. 5000 ng/ml trypsin Tothree of the tubes add 50 ul 5.0 × 10⁻³ mg/ml trypsin 9. 50,000 ng/mltrypsin To three of the tubes add 50 ul 5.0 × 10⁻² mg/ml trypsin 10.500,000 ng/ml trypsin To three of the tubes add 50 ul 5.0 × 10⁻¹ mg/mltrypsin 1-9 - received 9 mls PBS 10 - received 10 mls of PBS

For each standard or sample, the following was done:

Process repeated using sterile PBS in place of succinylated casein.These tubes served as blanks for the standards.

Incubated for 24 hrs at 40° C. in a shaking water bath.

Color Development

At the end of the 120 hrs period, samples were vortexed and centrifugedat 13,000 rpm for 10 min. 150 μl of supernatant was removed from eachsample and transferred to a 96 well ELISA plate.

TNBSA working solution was prepared by adding 100 ul of stock TNBSAsolution to 14.9 ml PBS.

In well A1 place 200 μl of water was placed as the path length plateblank.

50 μl of TNBSA working solution was added to all other wells.

Incubated for 20 min at room temperature.

Measured absorbance at 405 nm.

Subtracted the average absorbance of each sample group from thecorresponding blank.

Assessment of Depth of Demineralization

It may further be useful to assess the depth of demineralization ofsurface demineralized particles. Any suitable method, includingmeasurement by x-ray, by contact x-ray, by contact microradiograph, bystain, by embedding in polymer, be microscopic study, or other may beused.

In one method, the bone particle is placed in 3% basic fuchsin in orderto stain the demineralized surface. The bone particle is photographed,acquired with Adobe Photoshop 5.0, and analyzed with Image-Pro Plus 3.1.The actual depth of demineralization is calculated by measuring thelength (pixels) of the stained demineralized area at several locations(Dp and Dr) for each time point. The pixel measurements are averaged andconverted to millimeters.

XV. Uses

Therapeutic Uses

The osteoinductive composition or osteoimplant is intended to be appliedat a bone repair site, for example, a site resulting from injury, defectbrought about during the course of surgery, infection, malignancy, ordevelopmental malformation. The osteoinductive composition may be usedfor treatment of metabolic bone disease, bone healing, cartilage repair,spinal disc repair, tendon repair, repair of a defect created by diseaseor surgery, dural repair and may be further used in a wide variety oforthopedic, periodontal, neurosurgical, and oral and maxillofacialsurgical procedures. The osteoinductive composition or osteoimplant mayfurther be used in veterinary applications.

At the time just prior to when the osteoinductive composition orosteoimplant is to be placed in a defect site, optional materials, e.g.,autograft bone marrow aspirate, autograft bone, preparations of selectedautograft cells, autograft cells containing genes encoding bonepromoting action, etc., can be combined with the osteoimplant. Theosteoimplant can be implanted at the bone repair site, if desired, usingany suitable affixation means, e.g., sutures, staples, bioadhesives,screws, pins, rivets, other fasteners and the like or it may be retainedin place by the closing of the soft tissues around it.

The osteoinductive compositions may also be used as drug deliverydevices. In certain embodiments, association with the osteoinductivecompositions increases the half-life of the relevant biologically activeagent(s). In some embodiments, the drug delivery devices may be used todeliver osteoinductive growth factors. Other preferred agents to bedelivered include factors or agents that promote wound healing. However,the osteoinductive compositions may alternatively or additionally beused to deliver other pharmaceutical agents including antibiotics,anti-neoplastic agents, growth factors, hematopoietic factors,nutrients, an other bioactive agents described above. The amount of thebioactive agent included with the DBM composition can vary widely andwill depend on such factors as the agent being delivered, the site ofadministration, and the patient's physiological condition. The optimumlevels is determined in a specific case based upon the intended use ofthe implant.

Non-Therapeutic Uses

In addition to therapeutic uses involving implantation into a subject,the osteoinductive composition has a number of other uses. For example,it can be used to generate or culture cell lines, tissues, or organshaving osteogenic or chondrogenic properties. In particular, cells canbe removed from a donor and cultured in the presence of anosteoinductive composition. The invention includes such cells as well astissues and organs derived therefrom. The cells, tissues, or organs maybe implanted into the original donor after a period of culture in vitroor may be implanted into a different subject.

XVI. Conclusion

In certain embodiments, the osteoinductive compositions and associatedosteoimplants produce bone or cartilage in an animal model and/or inhuman patients with similar timing and at a level at least 10%, 20%,35%, 50%, 100%, 200%, 300%, or 400% or greater osteogenic,osteoinductive or chondrogenic activity than a corollary carrier thathas not been exposed to a treatment or condition as described herein.One skilled in the art will appreciate that these values may varydepending on the type of test used to measure the osteoinductivity orosteogenic or chondrogenic activity described above. The test resultsmay fall within the range of 10% to 35%, 35% to 50%, 50% to 100%, 100%to 200%, and 200% to 400%. In certain embodiments, when an osteoimplantis implanted into a bone defect site, the osteoimplant has anosteoinductivity score of at least 1, 2, 3, or 4 in an animal modeland/or in humans.

Although the invention has been described with reference to specificembodiments, persons skilled in the art will recognize that changes maybe made in form and detail without departing from the spirit and scopeof the invention.

1-91. (canceled)
 92. A method for producing an osteoinductivecomposition, the method comprising: providing bone particles; surfacedemineralizing the bone particles removing water from the boneparticles; providing pressed demineralized bone fibers; removing waterfrom the pressed demineralized bone fibers; and combining the surfacedemineralized bone particles and demineralized bone fibers.
 93. Themethod of claim 92, wherein surface demineralizing the bone particlescomprises demineralizing the bone particles to about 5 to about 99%demineralized.
 94. The method of claim 92, wherein surfacedemineralizing the bone particles comprises demineralizing the boneparticles to about 10 to about 50% demineralized.
 95. The method ofclaim 92, wherein surface demineralizing the bone particles comprisesdemineralizing the bone particles to about 10% demineralized.
 96. Themethod of claim 92, wherein providing pressed demineralized bone fiberscomprises providing pressed demineralized bone fibers having a medianlength to median thickness ratio of at least about 10:1 and up to about500:1, a median length of from about 2 mm to about 400 mm, a mediumwidth of about 2 mm to about 5 mm, and a median thickness of from about0.02 mm to about 2 mm.
 97. The method of claim 92, wherein providingpressed demineralized bone fibers comprises applying pressure tounconstrained demineralized bone.
 98. The method of claim 92, whereinproviding pressed demineralized bone fibers comprises mechanicallypressing demineralized bone which is constrained within a sealed chamberhaving at least one aperture.
 99. The method of claim 92, whereinproviding pressed demineralized bone fibers comprises applying pressureto unconstrained bone to form fibers, constraining the fibers in asealed chamber having at least one aperture, and mechanically pressingthe constrained fibers.
 100. The method of claim 92, wherein removingwater from the pressed demineralized bone fibers comprises criticalpoint drying the pressed demineralized bone fibers.
 101. The method ofclaim 92, wherein removing water from the surface demineralized boneparticles comprises lyophilizing the surface demineralized boneparticles.
 102. The method of claim 92, wherein removing water from thesurface demineralized bone particles comprises critical point drying thesurface demineralized bone particles.
 103. The method of claim 92,further comprising treating the surface demineralized bone particleswith supercritical carbon dioxide.
 104. The method of claim 92, whereinsaid demineralized bone particles and said pressed demineralized bonefibers are combined before the water is removed from them.
 105. Themethod of claim 92, wherein providing bone particles comprises providingxenograft bone particles.
 106. The method of claim 92, wherein the boneparticles are between about 0.5 and about 15 mm in their longestdimension.
 107. The method of claim 92, wherein the bone particles arebetween about 1 and about 10 mm in their longest dimension.
 108. Themethod of claim 92, wherein the bone particles are between about 1 andabout 8 mm in their longest dimension.
 109. The method of claim 92,wherein the bone particles are between about 0.5 and about 4 mm in theirlongest dimension.
 110. The method of claim 92, wherein the boneparticles are between about 1 and about 4 mm in their longest dimension.111. The method of claim 92, further comprising providing a deliveryvehicle and adding the surface demineralized bone particles anddemineralized bone fibers to the delivery vehicle.
 112. The method ofclaim 111, wherein the delivery vehicle is a carrier.
 113. The method ofclaim 112, wherein the carrier is a polyol, a polysaccharide, ahydrogel, or a polymer.
 114. The method of claim 112, wherein the polyolis glycerol.
 115. The method of claim 112, wherein the polysaccharide isa starch.
 116. The method of claim 112, wherein the hydrogel is chitosanor alginate.
 117. The method of claim 112, wherein the polymer ispolyethylene glycol.
 118. The method of claim 112, further comprisingmolding the surface demineralized bone particles, demineralized bonefibers, and carrier.
 119. The method of claim 111, wherein the deliveryvehicle is a covering.
 120. The method of claim 119, wherein thecovering is a mesh.
 121. The method of claim 119, wherein the coveringis tubular.
 122. The method of claim 119, wherein the covering isresorbable.
 123. The method of claim 119, wherein the surfacedemineralized bone particles and demineralized bone fibers are added tothe covering prior to implantation of the covering in the body.
 124. Themethod of claim 119, wherein the surface demineralized bone particlesand demineralized bone fibers are added to the covering afterimplantation of the covering in the body.
 125. The method of claim 92,further comprising sterilizing the surface demineralized bone particles.126. The method of claim 126, further comprising removing water from thesurface demineralized bone particles before sterilizing the surfacedemineralized bone particles.
 127. The method of claim 92, furthercomprising providing a tissue-derived extract and adding thetissue-derived extract to the surface demineralized bone particles. 128.The method of claim 128, further comprising packing the tissue-derivedextract and surface demineralized bone particles.
 129. The method ofclaim 128, wherein the tissue-derived extract is bone-derived,bladder-derived, kidney-derived, brain-derived, skin-derived, orconnective tissue-derived.
 130. The method of claim 130, wherein thebone from which the tissue-derived extract is derived from cortical,cancellous, or corticocancellous bone.
 131. The method of claim 130,wherein the bone from which the tissue-derived extract is derived iswaste bone.
 132. The method of claim 130, wherein the tissue-derivedextract is allogenic, autogenic, xenogenic, or transgenic.
 133. Themethod of claim 128, wherein the tissue-derived extract is a proteinextract.
 134. An implantable osteoinductive composition, the compositioncomprising: surface demineralized bone particles; pressed demineralizedbone fibers; and a delivery vehicle, wherein the surface demineralizedbone particles and the pressed demineralized bone fibers are providedwithin the delivery vehicle. 135-300. (canceled)